System for encoding resource access credential in barcode

A system including:

• a user device including:
• a display;
• at least one processor, wherein the processor is configured to:
• obtain a resource access credential authorising payment for a transaction relating to the purchase of goods or services;
• receive a user supplied transaction identifier from a user;
• generate a barcode encoding barcode data including at least a purchasing entity identifier, the resource access credential, and the user supplied transaction identifier;
• and
• display the barcode on the display of the user device;
• a merchant computing system including:
• an optical reader;
• at least one processor, wherein the processor is configured to:
• receive the barcode data from the optical reader on reading of the displayed barcode, in use;
• request payment for the transaction using the resource access credential;
• and
• produce a transaction data packet containing transaction data relating to the transaction, together with at least the purchasing entity identifier and the user supplied transaction identifier.