The FHIR server accepts a Bundle containing an Id, changes the value of the Id, and returns success.
FHIR Spec Section 2.1.0.13 states: “If the client wishes to have control over the id of a newly submitted resource, it should use the update interaction instead.” In fact, if we’re accepting the post and re-assigning the ID, we’re in violation of the spec ourselves, as it further states: “If an ID element is provided, the server SHALL respond with a HTTP 400 error code, and SHOULD provide an operation outcome identifying the issue.” .