Callback is only checking digest. If digest is mismatching, response will be HTTP 406.
- Callback is checking digest. If digest is bad, reply HTTP 406.
- Callback is checked, but the order is not there, reply HTTP 410.
- Callback is check, order is not there, but plugin is configured to allowed to accept the order as it existed, reply HTTP 210.
Response codes are based on https://developer.mozilla.org/en-US/docs/Web/HTTP/Status
406 = Not acceptable.
410 = Gone.
204 = No Content.
The responses are based on the fictive state of the order.