Hello, I am using VAPI with a Telnyx SIP connection and encountering a blocking issue with inbound audio. Setup: – VAPI + Voiceflow integration – Telnyx SIP for telephony – Calls connect successfully – AI voice (TTS) plays correctly Problem: – Incoming audio from the caller is not properly recognized – STT does not trigger or receives unusable audio – The conversation cannot proceed beyond the first message Additional context: – The issue appears to be related to inbound media quality or routing – Outbound audio is clear and consistent Questions: 1. Are there known compatibility issues between VAPI and Telnyx SIP? 2. What audio format / codec does VAPI expect for reliable STT? 3. Are there recommended telephony providers for stable two-way voice AI calls? 4. Is there any logging or debugging tool within VAPI to inspect incoming audio streams? Goal: Reliable, real-time voice interaction with accurate speech recognition. I can provide call examples and IDs if needed. Thank you, Zsolt

Suggestion: Check your Telnyx SIP trunk's codec settings and ensure only the following codecs are enabled: G711U (PCMU), G711A (PCMA), and OPUS. Disable any other codecs to avoid negotiation issues that can cause distorted inbound audio or STT failures. Example configuration:

Codecs:
- OPUS: enabled
- G711U (PCMU): enabled
- G711A (PCMA): enabled
- G729, G722, AMR-WB, etc.: disabled

This matches the recommended setup for real-time AI voice applications in the [official Vapi Telnyx SIP integration guide](https://docs.vapi.ai/advanced/sip/telnyx). Source: - [Telnyx SIP Integration Guide (Vapi Documentation)](https://docs.vapi.ai/advanced/sip/telnyx)

Hi, Sorry for the delay, please see: If inbound routing is configured, call your phone number from an external line. Ensure your provider forwards calls to the correct SIP URI: {phoneNumber}@.[sip.vapi.ai](http://sip.vapi.ai) ref: [https://docs.vapi.ai/advanced/sip/sip-trunk](https://docs.vapi.ai/advanced/sip/sip-trunk) Thank you