We are experiencing an issue with call transfers that is affecting usability.
When we transfer a live call from the AI to another person (cold transfer), the destination phone starts ringing correctly, but the call only stays active for around 5 seconds. After that, the transfer is automatically canceled, the call hangs up on the recipient side, and control returns to the AI voice.
Five seconds is far too short for a human to realistically pick up the call, especially for mobile or PSTN numbers. From the user’s perspective, the transfer appears to fail even though the destination phone was ringing normally.
We’ve confirmed that:
The call is successfully initiated and rings on the destination
There are no custom SIP headers involved
The issue appears to be a timeout during the transfer process rather than a routing or SIP provider problem
Is this transfer ringing timeout configurable on your side, or is there a recommended approach to allow the call to ring for a longer period before canceling?
Based on the available documentation, there is no explicit configuration for cold transfer ringing timeout in Retell AI’s transfer call settings(1). The documentation covers transfer number configuration, transfer type selection (cold vs warm), caller ID settings, and custom SIP headers, but does not mention a configurable timeout parameter for cold transfers specifically(1).
However, for warm transfers, Retell AI does provide an Agent Detection Timeout setting that controls the maximum time the AI will wait to determine whether the transfer target is human(1). This timeout defaults to 30 seconds, and the caller is only connected if human detection succeeds within this timeframe(1). If the timeout is exceeded, the transfer is marked as failed(1).
Since your issue involves a cold transfer with approximately 5 seconds before automatic cancellation, and this behavior is not documented as a configurable setting for cold transfers, I recommend:
Consider switching to warm transfer - This gives you explicit control over the agent detection timeout and ensures the destination has adequate time to answer(1)(2)
Check your SIP provider settings - Since Retell uses SIP REFER for cold transfers(1), the timeout behavior may be controlled at your telephony provider level rather than within Retell
Contact Retell support - Given that 5 seconds is unusually short and not mentioned in the documentation, this may be a provider-specific limitation or a configuration issue that requires direct assistance
For immediate resolution, warm transfer would allow you to configure the agent detection timeout up to your preferred duration, ensuring sufficient ring time before the transfer is considered failed(1)(2).