When an outbound call is made and a dial_failed, dial_busy, dial_no_answer reason is returned, it means that the outbound call is not successful. There can be a few reasons for this (we are adding more granular disconnection reasons to improve the visibility into why outbound call dialing fails starting july 1, 2025):

  • dial_failed:

    • The number dialed is not existent
    • The number you use to dial is marked as spam and got blocked (see below for more details)
    • Error met in telephony provider (for example, max call per second limit reached)
    • If using numbers purchased from Retell, dial to non US numbers are not supported.
    • if using custom telephony, it might be your outbound termination url & credential configuration issue.

  • dial_busy:

    • The number dialed is busy

  • dial_no_answer:

    • The number dialed did not answer

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Steps to troubleshoot

1

Check the call detailed log, it contains the SIP error code and the error message. Most cases this would be enough for you to identify the root cause.

2

If the call detailed log does not provide enough information, you can try the following:

  • If using custom telephony

    1. Double check your configuration and make sure you imported the right information. Refer to FAQ for more info.
    2. If the configuration is not correct, delete the imported number and re-import.
    3. If that does not solve it, please check with your telephony provider to see what’s the error on their side.

  • If using numbers purchased from Retell

    1. Check if the number is marked as spam.
    2. Make sure the destination number can accept the call. Currently numbers purchase from Retell can only make calls to US numbers.

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Number marked as spam

When a number experience high outbound call volume spike without any warmup, and / or has a low pickup rate, it might be marked as spam by carriers. When this happens, the number will get blocked frequently. To remedy this, you can try to:

  • Purchase a new number, and warm it up before pouring all traffic to it (slowly add outbound traffic to it)
  • Increase the pickup rate, read more at Increase Pickup Rate
  • register the number with our spam remediation feature, read more at verified phone number