Microsoft Exam PL-400 Topic 3 Question 49 Discussion

User5 receives the error message: 'Endpoint unavailable' during a test of the technician dispatch ISV solution.

When you choose to use a synchronous execution mode any failure will be reported back to the user of the application with an Endpoint unavailable error dialog informing the user that the webhook service endpoint may be configured incorrectly or is not available.

https://docs.microsoft.com/en-us/powerapps/developer/common-data-service/use-webhooks