SIPS NOT ALLOWED with 380 warning

[E2-Sterlin]

Question

I am currently utilizing Flexisip as a proxy server for Asterisk. Following the guidelines provided in the Flexisip documentation, I have successfully installed and configured the server to listen on TLS.
The Linphone client is able to establish a connection to Asterisk via Flexisip using TLS.
However, I am encountering issues when attempting to make calls. The following errors are being generated, and the calls are not being completed:
"480 Temporarily Unavailable"
"SIPS NOT ALLOWED" accompanied by a 380 warning
I would appreciate any insights or recommendations on how to resolve these issues to ensure successful call completion.