Surescripts makes up to 3 additional delivery attempts with a delay of at least 1 minute, 5 minutes and then 10 minutes between each attempt.
Right now callback is supposed to be used for NewRx and CancelRx only.
Endpoint expects a xml body with message. In a Header element there is RelatesToMessageID tag which have to contain a message id that was generated on transmit. You can find it in a relevant MedicationRequest identifiers, eg MedicationRequest.identifier.where(system = "urn:app:aidbox:e-prescriptions:surescripts:message-id").value.
For CancelRx there is same MedicationRequest used, so to distinguish between NewRx and CancelRx there is type specified, eg: