The 'payto' URI Scheme for Payments
A unified URI scheme for payment links that works with any payment system.
Dold, F. and C. Grothoff, "The 'payto' URI Scheme for Payments", RFC 8905, DOI 10.17487/RFC8905, October 2020, <https://www.rfc-editor.org/info/rfc8905>.
@misc{rfc8905,
series = {Request for Comments},
number = 8905,
howpublished = {RFC 8905},
publisher = {RFC Editor},
doi = {10.17487/RFC8905},
url = {https://www.rfc-editor.org/info/rfc8905},
author = {F. Dold and C. Grothoff},
title = {{The 'payto' URI Scheme for Payments}},
pagetotal = 12,
year = 2020,
month = oct,
} RFC text
Contents
Independent Submission F. Dold
Request for Comments: 8905 Taler Systems SA
Category: Informational C. Grothoff
ISSN: 2070-1721 Bern University of Applied Sciences
October 2020
The 'payto' URI Scheme for Payments
Abstract
This document defines the 'payto' Uniform Resource Identifier (URI)
scheme for designating targets for payments.
A unified URI scheme for all payment target types allows applications
to offer user interactions with URIs that represent payment targets,
simplifying the introduction of new payment systems and applications.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not candidates for any level of Internet Standard;
see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8905.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Table of Contents
1. Introduction
1.1. Objective
1.2. Requirements Language
2. Syntax of a 'payto' URI
3. Semantics
4. Examples
5. Generic Options
6. Internationalization and Character Encoding
7. Tracking Payment Target Types
7.1. ACH Bank Account
7.2. Business Identifier Code
7.3. International Bank Account Number
7.4. Unified Payments Interface
7.5. Bitcoin Address
7.6. Interledger Protocol Address
7.7. Void Payment Target
8. Security Considerations
9. IANA Considerations
10. Payto Payment Target Types
11. References
11.1. Normative References
11.2. Informative References
Authors' Addresses
1. Introduction
This document defines the 'payto' Uniform Resource Identifier (URI)
[RFC3986] scheme for designating transfer form data for payments.
1.1. Objective
A 'payto' URI always identifies the target of a payment. A 'payto'
URI consists of a payment target type, a target identifier, and
optional parameters such as an amount or a payment reference.
The interpretation of the target identifier is defined by the payment
target type and typically represents either a bank account or an
(unsettled) transaction.
A unified URI scheme for all payment target types allows applications
to offer user interactions with URIs that represent payment targets,
simplifying the introduction of new payment systems and applications.
1.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Syntax of a 'payto' URI
This document uses the Augmented Backus-Naur Form (ABNF) of
[RFC5234].
payto-URI = "payto://" authority path-abempty [ "?" opts ]
opts = opt *( "&" opt )
opt-name = generic-opt / authority-specific-opt
opt-value = *pchar
opt = opt-name "=" opt-value
generic-opt = "amount" / "receiver-name" / "sender-name" /
"message" / "instruction"
authority-specific-opt = ALPHA *( ALPHA / DIGIT / "-" / "." )
authority = ALPHA *( ALPHA / DIGIT / "-" / "." )
'path-abempty' is defined in Section 3.3 of [RFC3986]. 'pchar' is
defined in Appendix A of [RFC3986].
3. Semantics
The authority component of a payment URI identifies the payment
target type. The payment target types are defined in the "Payto
Payment Target Types" registry (see Section 10). The path component
of the URI identifies the target for a payment as interpreted by the
respective payment target type. The query component of the URI can
provide additional parameters for a payment. Every payment target
type SHOULD accept the options defined in generic-opt. The default
operation of applications that invoke a URI with the 'payto' scheme
MUST be to launch an application (if available) associated with the
payment target type that can initiate a payment. If multiple
handlers are registered for the same payment target type, the user
SHOULD be able to choose which application to launch. This allows
users with multiple bank accounts (each accessed via the respective
bank's banking application) to choose which account to pay with. An
application SHOULD allow dereferencing a 'payto' URI even if the
payment target type of that URI is not registered in the "Payto
Payment Target Types" registry. Details of the payment MUST be taken
from the path and options given in the URI. The user SHOULD be
allowed to modify these details before confirming a payment.
4. Examples
Valid Example:
payto://iban/DE75512108001245126199?amount=EUR:200.0&message=hello
Invalid Example (authority missing):
payto:iban/12345
5. Generic Options
Applications MUST accept URIs with options in any order. The
"amount" option MUST NOT occur more than once. Other options MAY be
allowed multiple times, with further restrictions depending on the
payment target type. The following options SHOULD be understood by
every payment target type.
amount: The amount to transfer. The format MUST be:
amount = currency ":" unit [ "." fraction ]
currency = 1*ALPHA
unit = 1*(DIGIT / ",")
fraction = 1*(DIGIT / ",")
If a 3-letter 'currency' is used, it MUST be an [ISO4217]
alphabetic code. A payment target type MAY define semantics
beyond ISO 4217 for currency codes that are not 3 characters. The
'unit' value MUST be smaller than 2^53. If present, the
'fraction' MUST consist of no more than 8 decimal digits. The use
of commas is optional for readability, and they MUST be ignored.
receiver-name: Name of the entity that receives the payment
(creditor). The value of this option MAY be subject to lossy
conversion, modification, and truncation (for example, due to line
wrapping or character set conversion).
sender-name: Name of the entity that makes the payment (debtor).
The value of this option MAY be subject to lossy conversion,
modification, and truncation (for example, due to line wrapping or
character set conversion).
message: A short message to identify the purpose of the payment.
The value of this option MAY be subject to lossy conversion,
modification, and truncation (for example, due to line wrapping or
character set conversion).
instruction: A short message giving payment reconciliation
instructions to the recipient. An instruction that follows the
character set and length limitation defined by the respective
payment target type SHOULD NOT be subject to lossy conversion.
6. Internationalization and Character Encoding
Various payment systems use restricted character sets. An
application that processes 'payto' URIs MUST convert characters that
are not allowed by the respective payment systems into allowable
characters using either an encoding or a replacement table. This
conversion process MAY be lossy, except for the instruction field.
If the value of the instruction field would be subject to lossy
conversion, modification, or truncation, the application SHOULD
refuse further processing of the payment until a different value for
the instruction is provided.
To avoid special encoding rules for the payment target identifier,
the userinfo component [RFC3986] is disallowed in 'payto' URIs.
Instead, the payment target identifier is given as an option, where
encoding rules are uniform for all options.
Defining a generic way of tagging the language of option fields
containing natural language text (such as "receiver-name", "sender-
name", and "message) is out of the scope of this document, as
internationalization must accommodate the restrictions and
requirements of the underlying banking system of the payment target
type. The internationalization concerns SHOULD be individually
defined by each payment target type.
7. Tracking Payment Target Types
A registry of "Payto Payment Target Types" is described in
Section 10. The registration policy for this registry is "First Come
First Served", as described in [RFC8126]. When requesting new
entries, careful consideration of the following criteria is strongly
advised:
1. The description clearly defines the syntax and semantics of the
payment target and optional parameters if applicable.
2. Relevant references are provided if they are available.
3. The chosen name is appropriate for the payment target type, does
not conflict with well-known payment systems, and avoids
potential to confuse users.
4. The payment system underlying the payment target type is not
fundamentally incompatible with the general options (such as
positive decimal amounts) in this specification.
5. The payment target type is not a vendor-specific version of a
payment target type that could be described more generally by a
vendor-neutral payment target type.
6. The specification of the new payment target type remains within
the scope of payment transfer form data. In particular,
specifying complete invoices is not in scope. Neither are
processing instructions to the payment processor or bank beyond a
simple payment.
7. The payment target and the options do not contain the payment
sender's account details.
Documents that support requests for new registry entries should
provide the following information for each entry:
Name: The name of the payment target type (case-insensitive ASCII
string, restricted to alphanumeric characters, dots, and dashes).
Description: A description of the payment target type, including the
semantics of the path in the URI if applicable.
Example: At least one example URI to illustrate the payment target
type.
Contact: The contact information of a person to contact for further
information.
References: Optionally, references describing the payment target
type (such as an RFC) and target-specific options or references
describing the payment system underlying the payment target type.
This document populates the registry with seven entries as follows
(see also Section 10).
7.1. ACH Bank Account
Name: ach
Description: Automated Clearing House (ACH). The path consists of
two components: the routing number and the account number.
Limitations on the length and character set of option values are
defined by the implementation of the handler. Language tagging
and internationalization of options are not supported.
Example:
payto://ach/122000661/1234
Contact: N/A
References: [NACHA], RFC 8905
7.2. Business Identifier Code
Name: bic
Description: Business Identifier Code (BIC). The path consists of
just a BIC. This is used for wire transfers between banks. The
registry for BICs is provided by the Society for Worldwide
Interbank Financial Telecommunication (SWIFT). The path does not
allow specifying a bank account number. Limitations on the length
and character set of option values are defined by the
implementation of the handler. Language tagging and
internationalization of options are not supported.
Example:
payto://bic/SOGEDEFFXXX
Contact: N/A
References: [BIC], RFC 8905
7.3. International Bank Account Number
Name: iban
Description: International Bank Account Number (IBAN). Generally,
the IBAN allows to unambiguously derive the associated Business
Identifier Code (BIC) using a lookup in the respective proprietary
translation table. However, some legacy applications process
payments to the same IBAN differently based on the specified BIC.
Thus, the path can consist of either a single component (the IBAN)
or two components (BIC followed by IBAN). The "message" option of
the 'payto' URI corresponds to the "unstructured remittance
information" of Single Euro Payments Area (SEPA) credit transfers
and is thus limited to 140 characters with character set
limitations that differ according to the countries of the banks
and payment processors involved in the payment. The "instruction"
option of the 'payto' URI corresponds to the "end-to-end
identifier" of SEPA credit transfers and is thus limited to, at
most, 35 characters, which can be alphanumeric or from the allowed
set of special characters, i.e., "+?/-:().,'". Language tagging
and internationalization of options are not supported.
Examples:
payto://iban/DE75512108001245126199
payto://iban/SOGEDEFFXXX/DE75512108001245126199
Contact: N/A
References: [ISO20022], RFC 8905
7.4. Unified Payments Interface
Name: upi
Description: Unified Payment Interface (UPI). The path is an
account alias. The amount and receiver-name options are mandatory
for this payment target. Limitations on the length and character
set of option values are defined by the implementation of the
handler. Language tags and internationalization of options are
not supported.
Example:
payto://upi/alice@example.com?receiver-name=Alice&amount=INR:200
Contact: N/A
References: [UPILinking], RFC 8905
7.5. Bitcoin Address
Name: bitcoin
Description: Bitcoin protocol. The path is a "bitcoinaddress", as
per [BIP0021]. Limitations on the length and character set of
option values are defined by the implementation of the handler.
Language tags and internationalization of options are not
supported.
Example:
payto://bitcoin/12A1MyfXbW6RhdRAZEqofac5jCQQjwEPBu
Contact: N/A
References: [BIP0021], RFC 8905
7.6. Interledger Protocol Address
Name: ilp
Description: Interledger protocol (ILP). The path is an ILP
address, as per [ILP-ADDR]. Limitations on the length and
character set of option values are defined by the implementation
of the handler. Language tagging and internationalization of
options are not supported.
Example:
payto://ilp/g.acme.bob
Contact: N/A
References: [ILP-ADDR], RFC 8905
7.7. Void Payment Target
Name: void
Description: The "void" payment target type allows specifying the
parameters of an out-of-band payment (such as cash or other types
of in-person transactions). The path is optional and interpreted
as a comment. Limitations on the length and character set of
option values are defined by the implementation of the handler.
Language tags and internationalization of options are not
supported.
Example:
payto://void/?amount=EUR:10.5
Contact: N/A
References: RFC 8905
8. Security Considerations
Interactive applications handling the 'payto' URI scheme MUST NOT
initiate any financial transactions without prior review and
confirmation from the user and MUST take measures to prevent
clickjacking [HMW12].
Unless a 'payto' URI is received over a trusted, authenticated
channel, a user might not be able to identify the target of a
payment. In particular, due to homographs [unicode-tr36], a payment
target type SHOULD NOT use human-readable names in combination with
unicode in the target account specification, as it could give the
user the illusion of being able to identify the target account from
the URI.
The authentication/authorization mechanisms and transport security
services used to process a payment encoded in a 'payto' URI are
handled by the application and are not in scope of this document.
To avoid unnecessary data collection, payment target types SHOULD NOT
include personally identifying information about the sender of a
payment that is not essential for an application to conduct a
payment.
9. IANA Considerations
IANA maintains the "Uniform Resource Identifier (URI) Schemes"
registry, which contains an entry for the 'payto' URI scheme as
follows. IANA has updated that entry to reference this document.
Scheme name: payto
Status: provisional
URI scheme syntax: See Section 2 of RFC 8905.
URI scheme semantics: See Section 3 of RFC 8905.
Applications/protocols that use this scheme name: payto URIs are
mainly used by financial software.
Contact: Christian Grothoff <grothoff@gnu.org>
Change controller: Christian Grothoff <grothoff@gnu.org>
References: See Section 11 of RFC 8905.
10. Payto Payment Target Types
This document specifies a list of payment target types. It is
possible that future work will need to specify additional payment
target types. The GNUnet Assigned Numbers Authority (GANA) [GANA]
operates the "Payto Payment Target Types" registry to track the
following information for each payment target type:
Name: The name of the payment target type (case-insensitive ASCII
string, restricted to alphanumeric characters, dots, and dashes)
Contact: The contact information of a person to contact for further
information
References: Optionally, references describing the payment target
type (such as an RFC) and target-specific options or references
describing the payment system underlying the payment target type
The entries in the "Payto Payment Target Types" registry defined in
this document are as follows:
+=========+=========+===========+
| Name | Contact | Reference |
+=========+=========+===========+
| ach | N/A | RFC 8905 |
+---------+---------+-----------+
| bic | N/A | RFC 8905 |
+---------+---------+-----------+
| iban | N/A | RFC 8905 |
+---------+---------+-----------+
| upi | N/A | RFC 8905 |
+---------+---------+-----------+
| bitcoin | N/A | RFC 8905 |
+---------+---------+-----------+
| ilp | N/A | RFC 8905 |
+---------+---------+-----------+
| void | N/A | RFC 8905 |
+---------+---------+-----------+
Table 1
11. References
11.1. Normative References
[ISO20022] International Organization for Standardization, "Financial
Services - Universal financial industry message scheme",
ISO 20022, May 2013, <https://www.iso.org>.
[ISO4217] International Organization for Standardization, "Codes for
the representation of currencies", ISO 4217, August 2015,
<https://www.iso.org>.
[NACHA] Nacha, "2020 Nacha Operating Rules & Guidelines", 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[unicode-tr36]
Davis, M., Ed. and M. Suignard, Ed., "Unicode Technical
Report #36: Unicode Security Considerations", September
2014.
11.2. Informative References
[BIC] International Organization for Standardization, "Banking
-- Banking telecommunication messages -- Business
identifier code (BIC)", ISO 9362, December 2014,
<https://www.iso.org>.
[BIP0021] Schneider, N. and M. Corallo, "Bitcoin Improvement
Proposal 21", September 2019, <https://en.bitcoin.it/w/
index.php?title=BIP_0021&oldid=66778>.
[GANA] GNUnet e.V., "GNUnet Assigned Numbers Authority (GANA)",
April 2020, <https://gana.gnunet.org/>.
[HMW12] Huang, L., Moshchuk, A., Wang, H., Schecter, S., and C.
Jackson, "Clickjacking: Attacks and Defenses", 2012,
<https://www.usenix.org/system/files/conference/
usenixsecurity12/sec12-final39.pdf>.
[ILP-ADDR] Interledger, "ILP Addresses - v2.0.0",
<https://interledger.org/rfcs/0015-ilp-addresses/>.
[UPILinking]
National Payments Corporation of India, "Unified Payment
Interface - Common URL Specifications For Deep Linking And
Proximity Integration", November 2017,
<https://www.npci.org.in/sites/default/files/
UPI%20Linking%20Specs_ver%201.6.pdf>.
Authors' Addresses
Florian Dold
Taler Systems SA
7, rue de Mondorf
L-5421 Erpeldange
Luxembourg
Email: dold@taler.net
Christian Grothoff
Bern University of Applied Sciences
Quellgasse 21
CH-2501 Biel/Bienne
Switzerland
Email: christian.grothoff@bfh.ch
AI ELI5
On this page
§1The Payto URI Scheme
The payto URI scheme provides a unified way to designate targets for payments. A payto URI always identifies the destination of a payment, which is typically either a bank account or an open transaction. The authority component of the URI identifies the payment target type (such as iban for IBAN bank transfers, bitcoin for Bitcoin addresses, or upi for India's Unified Payment Interface). The path component identifies the specific account or address within that payment system. Query parameters can specify optional details such as amount, payer name, recipient name, and a payment message.
By providing a single URI scheme for all payment systems, applications can offer consistent user interactions with payment links, and new payment systems can be added to a registry without requiring changes to every application.
A payto link is like a web link, but instead of pointing to a page, it points to a bank account or payment address. The link says what payment system is being used and what account to pay, and it can also include how much money to send and a message explaining why.
§2How Payto URIs are Structured
A payto URI follows the syntax: payto://authority/path?options. The authority must be an alphabetic string followed by alphanumeric characters, dots, or dashes; it identifies the payment target type and defines how the path should be interpreted. The path component is specific to each payment type and can include multiple segments separated by slashes (for example, an ACH payment includes both a routing number and account number in the path).
When an application handles a payto URI, it MUST first review the payment details with the user and get confirmation before initiating any financial transaction. The application SHOULD also prevent clickjacking attacks. If a payment target type is not recognized, the application MAY still allow the user to view and modify the payment details (the path and options) before proceeding.
A payto link has the form payto://paymenttype/account?options. The payment type tells you what system is being used (like iban for banks or bitcoin for Bitcoin). The account is the destination's address in that system. The options say how much money and any message to include.
payto://iban/DE75512108001245126199?amount=EUR:200.0&message=Invoice
payto://bitcoin/12A1MyfXbW6RhdRAZEqofac5jCQQjwEPBu
payto://ach/122000661/1234
payto://upi/alice@example.com?receiver-name=Alice&amount=INR:200
payto://void/?amount=EUR:10.5§3Payment Amounts and Standard Fields
All payment target types SHOULD support several standard options (generic options) that describe the payment itself. The amount option specifies how much money to transfer in the format currency:unit.fraction. A 3-letter currency code MUST be an ISO 4217 alphabetic code (such as EUR, USD, or INR). The unit value MUST be less than 2^53, and the fraction (if present) MUST have no more than 8 decimal digits. Commas may be included for readability and MUST be ignored.
The receiver-name option specifies the name of the entity receiving the payment (the creditor). The sender-name option specifies the name of the entity making the payment (the debtor). The message option provides a short message identifying the payment's purpose. The instruction option provides reconciliation instructions to the recipient (for example, an invoice number or reference code). All of these options MAY be subject to lossy conversion, modification, or truncation due to character set limitations in the underlying payment system, except that the instruction field SHOULD NOT be truncated if possible.
The options in a payto link can say how much money to send (like EUR:100.00), who is paying, who is receiving, and what the money is for (like "Invoice 123").
§4Different Payment System Types
The RFC defines seven payment target types: ach for Automated Clearing House (US bank transfers), bic for Business Identifier Code (for wire transfers between banks), iban for International Bank Account Number (used throughout Europe and many other countries), upi for Unified Payment Interface (India's mobile payment system), bitcoin for Bitcoin addresses, ilp for Interledger Protocol addresses, and void for out-of-band payments like cash.
Each type has different requirements and limitations. For example, IBAN allows an optional BIC component for legacy systems. UPI requires the amount and receiver-name options. Bitcoin uses addresses as defined in BIP 21. The void type allows specifying payment parameters for transactions that happen outside the internet, such as in-person cash payments.
New payment types can be registered in the Payto Payment Target Types registry using a First Come First Served policy.
The RFC shows how to write payto links for seven different payment systems: bank transfers in the US (ACH) and Europe (IBAN), wire transfers (BIC), India's payment app (UPI), Bitcoin, a newer protocol (ILP), and cash payments.
§5Handling Different Languages and Character Sets
Many payment systems use restricted character sets. Applications that process payto URIs MUST convert characters that are not allowed by the target payment system into allowable characters, either by encoding or replacement. This conversion process MAY be lossy for most options, but the instruction field (which is used for payment reconciliation) SHOULD NOT be truncated if possible.
If converting the instruction field would cause lossy conversion, modification, or truncation, the application SHOULD refuse to proceed with the payment and ask the user to provide a different instruction value.
The payto scheme disallows the userinfo component (username and password) in URIs to avoid special encoding rules. Instead, payment details are passed as query options, where encoding rules are uniform across all options.
Different payment systems accept different letters and symbols. When an application sends a payto link to a payment system, it may need to change special characters to ones that system accepts. If important information like a reference code would get mangled, the application should ask the user to change it first.