In the ProCall mobile app for Android, a call is made via the softphone line, but the smartphone dials via GSM.
The behavior occurs when ProCall is enabled as a call account in Android and a Sophos MDM (Mobile Device Management) is in use.
Sophos seems to interfere when another app is activated as a call account and only allows dialing via GSM.
Checking possible causes
Check that the Sophos MDM app is installed on the smartphone.
Check if ProCall is enabled as a call account in the Android system.
Example screenshot: Check call account – Line settings – Android call account
Deactivate ProCall as Android call account and use the ProCall mobile in-app call window.