The Payer-to-Payer API describes the FHIR resources as a set of operations (known as "interactions") on resources where individual resource instances are managed in collections by their type. The CapabilityStatement specifies only two interactions: Read and Search.
Read (Fetch) Syntax
Please see the official HL7 FHIR documentation to understand the read syntax: https://www.hl7.org/fhir/http.html#read
Search Syntax
Please see the official HL7 FHIR documentation to understand the search syntax: https://www.hl7.org/fhir/http.html#search
Response Status Code
Please see the official HL7 FHIR documentation on status codes: https://www.hl7.org/fhir/http.html#Status-Codes
Response Format
At this time, the PayerToPayer API supports only responses containing JSON.