Call transfer failing

Support Help
1

Call transfer failing from time to time, nothing on the end of the transfer line has changed at all.

Sometimes it fails, sometimes it goes through. Makes 0 sense.

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2

Intermittent call transfer failures can occur due to several factors. When call transfer is triggered but fails, the most common causes are telephony issues and human detection problems(1).

Telephony Issues

Call transfer behaves similarly to placing an outbound call, and failures occur for similar reasons as outbound call failures(1). The SIP connection log available in your call logs is useful for diagnosing the failure reason(1).

Human Detection Issues

If human detection is enabled, the call may fail if a human is not successfully detected(1). Possible reasons include:

  • No human was actually present (e.g., it was an IVR or voicemail)(1)
  • The other party spoke, but only after the detection timeout expired(1)
  • The speech was too similar to an IVR or voicemail and was not recognized as human(1)

Configuration to Check

For warm transfers specifically, verify your Agent detection timeout setting, which is the maximum amount of time the AI agent will wait to determine whether the transfer target is a human(2)(3). The caller is connected only if human detection succeeds within this timeframe; otherwise, the transfer is marked as failed(2)(3). The default timeout is 30 seconds(2)(3).

Recommended Actions

  1. Review the SIP connection logs for the failed calls to identify the specific failure reason(1)
  2. Check your human detection settings and consider adjusting the agent detection timeout if calls are timing out(2)(3)
  3. Verify that your transfer destination number is in the correct format (e.164 format or SIP URI format like sip:username@domain)(2)(3)

If the issue persists after checking these settings, the SIP logs should reveal the underlying telephony provider issue causing the intermittent failures.

3

Hello @Quetalk

Can you share the call id for this call?

5

call_5fc461d1be2461bf58ae5a18823

Let me know if you need anything else.

6

To investigate the specific call transfer failure for call_5fc461d1be2461bf58ae5a18823, I’d need access to the call logs and SIP connection details in your Retell AI dashboard, which I don’t have direct access to.

However, based on the call ID you’ve provided, here’s what you should check:

Steps to Debug This Specific Call

  1. Check the SIP Connection Log - Navigate to your call logs in the Retell AI dashboard and locate call call_5fc461d1be2461bf58ae5a18823(1). The SIP connection log is available in the call logs and is useful for diagnosing the failure reason(1).

  2. Review the Disconnection Reason - Look for the specific error code or disconnection reason in the call details. Common telephony-related errors include SIP routing errors, provider unavailability, or the call being marked as spam(1).

  3. Verify Human Detection Settings - If human detection is enabled for this transfer, check whether:

    • A human was actually present (vs. IVR or voicemail)(1)
    • The other party spoke before the detection timeout expired(1)
    • The speech pattern was recognized as human and not confused with IVR/voicemail(1)

Configuration Review

Since you mentioned nothing changed on the transfer destination end, verify your agent’s transfer configuration:

  • Agent detection timeout: Confirm it’s set appropriately (default is 30 seconds)(2)(3)
  • Transfer number format: Ensure it’s in e.164 format or SIP URI format (sip:username@domain)(2)(3)
  • Caller ID settings: Check if caller ID override is configured and supported by your telephony provider(2)(3)

The intermittent nature suggests either network/telephony provider issues or timing-related problems with human detection. The call logs for this specific call ID should reveal the exact cause.

If you need further assistance analyzing the logs, you can:

7

Hello @Quetalk

You are getting 603 SIP error category: user_declined

Which means that the user rejected your call or the provider did

8

The SIP error code 603 with user_declined disconnection reason means the call was explicitly declined(1). This can happen when either the user manually declined the call or the telephony provider rejected it(1).

For your specific situation with cold calling in America where all calls are going to user_declined and not_connected, the most likely cause is that your number has been marked as spam(1)(2). When a number experiences high outbound call volume spikes without warmup and has a low pickup rate, it might be marked as spam by carriers(2). When this happens, the number will get blocked frequently(2).

To remedy this, you can:

  • Purchase a new number and warm it up before pouring all traffic to it (slowly add outbound traffic)(2)
  • Increase the pickup rate(2)
  • Register the number with Retell’s spam remediation feature using verified phone numbers(2)

The team confirmed that your Retell number is considered spam from Twilio(3). The number may be recoverable by verifying it or using a branded call display, but this cannot be guaranteed(3). The team recommends getting a new phone number(3). To maintain a healthy reputation, avoid practices like short calls or generating complaints from end users(3).