curl -v -H "accept: application/fhir+xml" -X GET "http://fhirserver/Appointment/?_id=Appointment-Read-Example" 

{"empty": false}

{
  "locationCol": 1706,
  "severity": "INFORMATION",
  "locationString": "Appointment.participant[0]",
  "locationLine": 1,
  "message": "This element does not match any known slice defined in the profile https://gematik.de/fhir/isik/StructureDefinition/ISiKTermin|5.1.2"
}

{
  "locationCol": 1204,
  "severity": "WARNING",
  "locationString": "Appointment.priority.extension[0].value.ofType(CodeableConcept)",
  "messageId": "Value set https://gematik.de/fhir/isik/ValueSet/ISiKTerminPriority has been ignored due to module configuration",
  "locationLine": 1,
  "message": "Value set https://gematik.de/fhir/isik/ValueSet/ISiKTerminPriority has been ignored due to module configuration"
}

{
  "locationCol": 1212,
  "severity": "INFORMATION",
  "locationString": "Appointment.priority.extension[0].value.ofType(CodeableConcept).coding[0]",
  "messageId": "Terminology_PassThrough_TX_Message",
  "locationLine": 1,
  "message": "Code system definition is missing for 'http://snomed.info/sct#394848005'"
}