First section

Nexo Standards

Our standards, based on universal and open ISO 20022 messages,
ensure the interoperability of payment acceptance

The benefits
of ISO International

ISO International Standards ensure the quality and reliability
of goods and services.

For businesses, they are strategic tools and guidelines to help companies tackle some of the most demanding challenges of modern business. They ensure that business operations are as efficient as possible, increase productivity and help companies access new markets. For government, ISO standards draw on international expertise and experience and are therefore a vital resource  when developing public policy.

second section




ISO 20022 is a common methodology used within the financial industry to create consistent messages across different subdomains of the industry. Its methodology is based on concept of separate layers with the business and the logical messages making up two different layers. The third layer, the syntax, is the physical representation of the logical message.

ISO 20022 makes a clear distinction between the way of representing the elements of information (the standards itself) and the actual representation of this information in a format or a language (the syntax or coding) that the machine can interpret. 

Each message is built along: a set of syntax and message design rules; message components; coding elements associated to the message components.
Provides a common platform for the development of messages using: a model methodology (based on UML); a central dictionary of business items (ISO 20022 Repository); a set of design rules to convert the messages described into a specific coding syntax, such as XML.



The ISO 20022 standard offered a way to shield investments from future syntax changes by encouraging users to build business transactions and message models under an internationally agreed upon approach, and to migrate to the use of a common vocabulary and a common set of syntaxes.


ISO 20022 brings profound benefits to the financial services industry, as it achieves end-to-end processing across domains and environments that previously used different standards and formats. The reusability of existing data components as well as the issuance of new components meeting the specific requirements of card payments offer a major benefit associated with the ISO 20022 methodology.


Why ISO 20022


  • A state-of-the-art methodology
  • A strong enabler of interoperability in the build-up of standards
  • A solution that provides independence between the definition of the message (standard) and its implementation (syntax)
  • Open and free of charge standards with a clear and transparent Intellectual Property Rights (IPR) policy
  • The strength of a universal ISO standard
  • A coherent approach, thanks to its convergence with other categories of financial messages
    and payment instruments, namely the ISO 20022-based SCT and SDD series of messages

Third section



Basically, a protocol is a set of rules and specifications to enable two or more entities to exchange information.

The nexo standards series of protocols belongs to the category of application protocols that govern the interaction and exchange of data between software applications where the exchange of data is performed between two different pieces of equipment:

  • The payment terminal (or a payment server) located usually at the merchant’s location
  • A server under the supervision of a bank, payment service provider, or entity acting on their behalf They also rely on the use of lower level data transport protocols to ensure that the exchange of information is carried out in a smooth, secure way.

In the domain of card payments, a protocol enables, among other things, the exchange of information to:

  • Authorize a card payment transaction
  • Cancel a card payment transaction
  • Allow a retailer to be credited for the payment transaction
  • Initiate the debiting of the customer (cardholder) account by the bank.



The nexo standards porfolio of protocols has been designed specifically to adress the lack of open and common specifications today on the market.



nexo Implementation Specification Package serve as a guideline and provides implementers all the documentations needed to develop nexo compliant solutions. It describes how a payment acceptance solution should be interacting with an Acquirer Host, a Terminal Management System (TMS) Host or a Sale System using nexo FAST Specification and nexo Protocols.

It includes deliverables (published specifications) for each specification or standard included in the nexo implementation scope :

Terminal Payment Application Specifications

Specifications on how to manage security

ISO 20022
Card Payment Exchange Protocols

Implementation specifications


nexo FAST is based on EMV Chip and PIN technology and describes unambiguously the financial application on a terminal which is compliant to the SEPA Cards Framework (SCF) of the European Payments Council (EPC) and also meets the functional requirements in the SEPA Cards Standardisation Volume Book of Requirements. nexo FAST has been developed with the objective of:
  • Supporting a uniform "look and feel" of transactions from the cardholder’s perspective
  • Reducing the risks of interoperability obstacles between applications
  • Enabling an open market for EMV-based components
  • Serving as the basis for a "one-stop shopping" for terminal testing and mutual recognition of type approval
  • Describing unambiguously the financial application on the SCF compliant terminal
The nexo FAST architecture and interfaces are defined on a logical level. Do not require a specific hardware or software architecture. It also Introduce the major concepts of interaction with the acquirer host, the sale system through: HAP -The interface to the Host Acquirer Protocol application and SCAP - The interface to the Sale System, Cardholder and Attendant Protocol application.
The nexo FAST application internal structure main functional blocks are: Terminal and Card Service Initiation; Card Service Processing and; Card Interaction Layer including Kernel processing.

Deliverables (published specifications) for each standard included in the nexo implementation scope include:

  • POI Payment Application Specifications
  • Specifications on how to manage security
  • Integration/usage of the ISO 20022 Card Payment Exchange Protocols
  • Implementation specifications
  • Test Plans for the POI Payment Application and the Acquirer Host incoming interface

A standardize approach with embeded security in the protocols

The “Card Payment Protocols Security” contains the specifications of the security mechanisms to secure the following nexo protocol messages:

  • nexo Acquirer protocol (ISO 20022 CAPE messages – ‘caaa’)
  • nexo TMS protocol (ISO 20022 CAPE messages – ‘catm’)
  • nexo Retailer protocol (Sale to POI protocol)

The protocol offers a next generation international card payment standard that replaces ISO 8583 and its national derivatives. The standard allows the use of real time or batch submission as well as supporting direct connections from merchant to acquirer or via a Payment Service Provider (PSP) intermediary.

The nexo Retailer protocol defines a set of interfaces between a card payment application and a retail point of sale system. It offers new innovative features such as a clear separation between sale and payment, the provision of a complete series of payment and loyalty services as well as a common approach for all types of architectures and environments.

The nexo TMS protocol is the first international standard for terminal management. This open, universal, non-proprietary TMS standard prevents retailers becoming locked-in to suppliers. It supports mixed estates and allows additional functionality to be incorporated. The ability to delegate authority, allowing multiple parties to fulfill differing aspects of terminal management, is innovative and most helpful to both merchants and merchant acquirers. As an ISO 20022 standard it will ease integration with other card processing systems.

The nexo ATM protocol is the first universal standardisation initiative related to the ATM transaction and management domain enabling the delivery of ISO 20022 ATM messages to both the financial and ATM manufacturing industries.