Confirm you are implementing the CDex STU2+ $submit-attachment operation — this is a system-level or base-URL operation, not a Claim-instance operation.
Construct a Parameters resource containing: AttachTo (the claim or prior auth reference), request (the X12 277ADRD or payer-assigned TrackingId), payerId, and one or more Attachment parameters each holding a DocumentReference or Binary resource.
POST the Parameters resource to [base]/$submit-attachment where [base] is the payer's FHIR server base URL (e.g., https://payer.example.org/fhir/$submit-attachment) — not [base]/Claim/$submit-attachment.
Handle the HTTP 200 response with a Parameters body; check for OperationOutcome inside the response to detect business-level rejections even on HTTP 200.
Retain the correlation identifiers returned so you can reconcile submission with the eventual adjudication or prior authorization decision.
Known gotchas
The operation is invoked at the system (base) level — POST [base]/$submit-attachment — not on a Claim instance; routing to [base]/Claim/$submit-attachment will likely return 404 or be ignored by the payer.
The CDex specification is under active development; always check the current HL7 CDex IG publication for the canonical operation definition URL and required parameters before implementation.
Payers may impose additional business rules on content type, attachment size, or required metadata beyond what the IG mandates — consult the payer's companion guide.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp