It looks like I found a bug in the API that deletes a phone number:
https://developers.telnyx.com/docs/api/v2/numbers/Number-Configurations?lang=node#deletePhoneNumber
The code is very simple and it was copied from example snippet as is. It throws the error:
TelnyxResourceNotFoundError: (Status 404) Resource not found
I use Node library. But I also tried to use REST. Both methods throw the same error. Could anyone check that please?