Since notifications use  history  type Bundles, a few additional elements need to be filled out in notifications. Specifically, the Bundle resource includes two constraints, bdl-3 and bdl-4 , which require entry.request and entry.response to be present on on every Bundle.entry . In order to meet these requirements, the status resource ( entry [0] ) SHALL have entry.request as a request to the  $status  operation (e.g., http://example.org/fhir/r4/subscription/id-123/$status ) and SHALL have entry.response with a status of 200 .