3CX Version: Professional Annual, 18.0 (Build 314)
Server OS: Debian 10 from AWS Marketplace
Is the 3CX Server Hosted and where?: AWS EC2 instance, us-west-2
IP Phone Make/Model/Firmware version: Softphone (3CX iOS App, v10.7.17)
Provisioning Method: Using QR code scanned within the iOS app
Trunk Provider or VoIP Gateway Make/Model: Telnyx SIP Trunk
Has the Firewall Checker passed: YES
Are custom Phone Templates being used: NO
Inbound calls appear normally, however when a client attempts to answer the call, the 3CX app gives a 3-tone error signal and then immediately after it starts ringing again. From the caller's side it continues to ring normally as if no-one attempted to answer. This is a single SIP trunk with two phone numbers and both numbers are listed in the 3CX server under SIP trunk -> DIDs. On the Telnyx side, both numbers are assigned to the SIP connection. This behavior happens on both lines. TLS is being used for the transport protocol, and the TLS root cert has been installed.
To try to narrow down the cause of the issue try pointing the inbound rule to a voicemail box of an extension and see if the call can be answered by the system. Also try answering the call from a 3CX Webclient or Desktop app and see if that works so we know at which point the issue occurs.
