• Is the endpoint active and subscribed to the event? Check it in Settings → Developer.
• Does your server answer quickly? Orbinly waits about 5 seconds for a response. Reply immediately and do slow work afterwards.
• Look at recent deliveries on the Developer page to see what was sent and the result.
• Failed deliveries are retried, up to 5 attempts, with a daily safety-net sweep.
• Signature check failing? Compute the HMAC-SHA256 of the raw request body with your endpoint's secret and compare it to X-Orbinly-Signature. Use the raw bytes, not re-serialized JSON.
• Requires Starter or above.

The reference is in the API & webhooks docs.