General Usage of ISO 20022

This guide defines the message standards that consists of message elements:

• required in the Nexus Scheme Rulebook as business requirements

• needed for processing by Payment Service Providers (PSPs) and Instant Payment Systems (IPS)

These message elements define the Nexus service and are denoted in the specific ISO 20022 Nexus message guidelines. This section describes the relevant Nexus requirements, such as the use of the message element, its components or the values that must be used. Usage rules, for example, may indicate limits on the number of repetitions, or code value restrictions, while format rules may be used to indicate the allowable combinations of components of a message element.

Only ISO 20022 messages are accepted

Nexus expects and will only accept the Nexus-standard ISO 20022 messages (and JSON APIs as defined by Nexus). These messages are based on the CPMI ISO 20022 harmonisation requirements and CBPR+ usage guidelines. The Nexus Usage Guidelines adds additional requirements necessary for processing Nexus payments.

Where an IPS community either (a) does not support ISO 20022 messages, or (b) uses elements differently than defined in the Nexus usage guidelines, then the IPSO is responsible for translating messages to be consistent with the Nexus usage guidelines. See Translation To/From Domestic Message Formatsfor further detail.

Accepted Message Set

With the exception of some JSON API calls, most communication through Nexus is done using messages following the ISO 20022 standard. The following ISO 20022 messages are implemented in the first release of Nexus:

• pacs.008.001.13 FI to FI Customer Credit Transfer

  • This is the basic payment instruction

• pacs.002.001.15 FI to FI Payment Status Report

  • This is the payment status report returned in response to a pacs.008

• acmt.023.001.04 Identification Verification Request

  • Used for proxy resolution and account resolution requests – see Addressing & Proxy Resolution.

• acmt.024.001.04 Identification Verification Response

  • Used for responses to proxy resolution and account resolution requests.

• pacs.028 FI to FI Payment Status Request

  • Request for an update on the status of a previously sent pacs.008 payment instruction

• camt.056 FI to FI Payment Cancellation Request

  • In Nexus, a cancellation message is used to cancel a High-Priority Payment which has not been confirmed or rejected by the Destination IPSO within the SLA.

• camt.029 Resolution of Investigation

  • This is the optional positive response sent in reply to a camt.056 Payment Cancellation Request

Version

Nexus uses the 2025 version of the ISO 20022 XML message standards. This is version 13 for the pacs.008 and version 15 for the pacs.002.

Backwards compatibility

Nexus will support backwards compatibility on a best effort based.

Character Set

The efficient processing of cross-border payments depends on the use of a common character set so that all participants in the processing chain will be able to understand and interpret the information. Otherwise, payments risk being delayed or even returned.

Following CPMI harmonization requirements, Nexus prescribes the use of a restricted character set in its cross-border payment messages to the currently agreed Latin character set: lower case characters a–z, upper case characters A–Z, numeric characters 0–9, complemented with the following additional characters for a limited selection of data elements:

/ - ? : ( ) . , ’ + ! # & % * = ^ _ ` { | } ~ " ; @ [ \ ] $ > <

References, identifications and identifiers must respect the following:

• Content is restricted to the Latin character set as defined above

• Content must not start or end with a forward slash ‘/’

• Content must not contain a double forward slash ‘//’

Message Validation

Messages sent to Nexus will be validated against the requirements in the Nexus message usage guidelines. Messages will fail validation in the following cases:

• The message does not conform to the Nexus XSD validation. In this case, Nexus will reject the message with error code FF01.

• An element that is defined as “Mandatory” in the Nexus usage guidelines is empty or null, or the entire element is missing from the message structure. In this case, Nexus will reject the message with error code CH21.

• An element that requires a code from the ISO 20022 External Code set in the <Cd> element instead uses the <Prtry> (Proprietary) element. In this case, Nexus will reject the message with error code CH21.

• An element that requires a code from the ISO 20022 External Code set uses a code that is not in the External Code Set. In this case, Nexus will reject the message with the applicable error code.