### Answer When calls ring once and hang up without appearing in Retell's call history, this typically indicates the call isn't reaching Retell's system [(1) ]() . Here are the key troubleshooting steps: Check your telephony provider first: Since the call doesn't appear in Retell's call history, the issue is likely at your telephony provider level . Check your provider's call logs (Twilio, Telnyx, etc.) to see if the call is reaching them and where it's failing . For SIP Trunking setups: If you're using SIP trunking, verify your configuration [(2) ]() : - Ensure your SIP trunk is pointing to

sip:sip.retellai.com

- Confirm your firewall allows traffic from Retell's IP blocks:

18.98.16.120/30

,

3.42.144.0/23

,

143.223.88.0/21

, and

161.115.160.0/19

- Check that you're using the correct transport method (TCP is recommended) For imported numbers: If you imported a number into Retell, verify [(3) ]() : - The number has an Inbound Call Agent assigned in your phone number settings - If using an inbound webhook, ensure it returns a successful 2xx status with the correct

override_agent_id

- If the inbound webhook fails and no default agent is set, calls will disconnect Common disconnection reasons: If calls were reaching Retell but disconnecting, you'd see these in call history with reasons like

dial_failed

,

dial_no_answer

, or

invalid_destination

[(4) ]() . Since you're not seeing any history, the calls aren't reaching Retell at all [(1) ]() . Start by checking your telephony provider's logs to trace where the call is stopping .

​ To learn more, see the sources I considered: [[1] Issue with Inbound Voice Agent](https://discord.com/channels/1186424376300679209/1413628905235021887) [[2] Connect Retell voice agents to custom telephony](https://docs.retellai.com/deploy/custom-telephony) [[3] Inbound call & SMS webhook](https://docs.retellai.com/features/inbound-call-webhook) [[4] Debug call disconnection](https://docs.retellai.com/reliability/debug-call-disconnect) ​

Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.