Based on your configuration, here are several areas to verify for your inbound SIP trunk setup:
Phone Number Format
Ensure your phone number is imported in E.164 format, which includes the country code prefixed with a plus sign (+), followed by the number with no spaces or special characters(1). For example, an Italian number should be formatted as "+39123456789"(1).
Termination URI Configuration
Your Termination URI should include the sip: prefix(2). The correct format should be sip:sip.messagenet.it:5060(2).
For inbound calls, you may also need to specify the transport method by appending it to the URI(2):
- For TCP:
sip:sip.messagenet.it:5060;transport=tcp(2) - For UDP:
sip:sip.messagenet.it:5060;transport=udp(2) - For TLS:
sip:sip.messagenet.it:5060;transport=tls(2)
Authentication Configuration
When importing your number via the Import Phone Number API, you need to supply the username and password in the sip_trunk_auth_username and sip_trunk_auth_password fields(3). Double-check that your SIP trunk credentials match exactly what’s configured with your provider(3).
Origination Settings
For inbound calls, you need to configure the origination settings in your SIP trunk provider to point to Retell’s SIP server(2):
- Retell SIP server URI:
sip:sip.retellai.com(2) - IP block for traffic:
18.98.16.120/30(All regions)(2)
Your provider needs to route inbound calls to Retell’s SIP server, not the other way around(2).
Common Disconnection Reasons
If calls show as dial_busy, this indicates the number dialed is busy(4). If you see telephony_provider_permission_denied, the SIP trunk credentials are not authenticated(4).
Next Steps
Check your origination setting in your SIP trunking provider and review the logs there(2). For urgent support, you can reach out via: