PSTN call transfers not working

Hello Teams Community,

Please I need your help on this.

we are having issues transferring incoming PSTN calls that come in through an Auto-attendant and Call queue and are answered by an employee and being transferred to an external PSTN number with the consultive transfer.

The employee that answered the call on their Teams client gets an error that the transfer is not working, and after that they are left with 2 windows with the 2 seperate calls.

They are not having this problem when transferring with internal users. We also own the SBC infrastructure, and we cannot see any error there.

Transfers without consulting, cold transfers, are working. You could see this behaviour at the call with the ID: 8ec345aa-7818-46a3-8172-8d875cf59eff