Subject: PSTN Call Transfer Failing — transfer_call returns success: false

Support Help
1

Hi Retell Support,

We’re using Retell for outbound patient outreach calls and have a
transfer_call tool configured to cold-transfer patients to our
clinic’s scheduling line at +19043230954.

The transfer consistently fails with success: false. We’ve tested with
both SIP INVITE and SIP REFER — same result. The call itself connects
fine, but when the patient agrees to be transferred and the tool
executes, it fails immediately.

Account details:

  • Outbound number: +19046641405
  • Transfer destination: +19043230954 (our clinic’s regular PSTN
    number, not a Retell number)
  • Transfer type: Cold Transfer
  • SIP method tested: SIP INVITE and SIP REFER

Example call IDs where transfer failed:

  • call_be5c0143dd104fdc5fc9cde1c
  • call_6228e2c357881d180456e620925

Could you confirm whether PSTN cold transfer to external numbers is
enabled on our account, and if not, how to enable it?

Thanks

2

Hello @vasislav70001abv.bg

Thank you for the details and Call IDs. I’ve forwarded them to our team for review.

We’ll get back to you as soon as we have an update.

Best regards

3

Hey @vasislav70001abv.bg

It looks like both call IDs are invalid. Could you please double-check and resend the correct call IDs?

Thank You

4

Hey @mark1,

Thank you for the quick response.

This is one example call_a260348063a666fd4fb01c6032e

The issues is that we tried to transfer the call to a number but it did not work.

Eg we call someone and they want to speak to a person then we send then to another number that persons responds.

Thanks!

5

Hey @vasislav70001abv.bg

It looks like the phone number does not have a SIP Trunk Username and Password configured. This is required for proper SIP connectivity.

You can see our (Twilio - Retell AI) guide to configure this.

Thank You

6

Hey @mark1

Were you saying that our phone number (the one that we use to call people) is not configured in twillio properly or the number we are trying to transfer them to?

Thanks!

7

Hey @vasislav70001abv.bg

The phone number itself in retell has no username or password.

Thank You

8

Hey @mark1,

I added the username and password but the transfer still didn’t go through.

Session id: call_00eea1a404270d7921721328ae5

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9

Hey @mark1,

Apologies if I’m being pushy, but I really need you help!

Regards,
Vas

10

Hello @vasislav70001abv.bg

This call is from the web, you can’t do call transfer from web.

Thank You

11

Hey @mark1,

Just tried with a live call but I had the same issue call_4840bb2eebc69d774f4f9122ef1.

Can you please take a look!

Regards,
Vas

12

Hey @vasislav70001abv.bg

If the issue is occurring after entering the username and password, it’s possible the credentials you entered are incorrect.

Kindly see our (https://youtu.be/JC3PV_R-Z1Y?si=H2dKyMXxuraDXiq_) video to connect your Twilio with Retell.

Thank You

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