Worked on the NHSDigital/e-referrals-service-api repository to enhance the API schema for improved traceability and identification of referrals and communications. Delivered a non-breaking schema evolution by introducing an identifier field, structured as an array of system and value objects, to both ReferralRequest and CommunicationRequest resources within the FHIR STU3 component. This addition enables unique identification through ers-request-id, supporting better auditability, reconciliation, and downstream analytics. The work involved careful schema definition and API development using YAML, with updated examples to illustrate identifier usage. No major bugs were addressed during this period, focusing solely on robust schema enhancement and maintainability.