Have you checked the Management Console's Event log too? What do you see there? It may be what @bitn2 and it is the SIP Provider rejecting the call.The phone calls exactly the number +491520xxxx. In the 3CX Call History I can see this call also with this number and the status is "not acepted".

No worries!Sorry, for speaking german.
Glad to see you got this sorted! I'll be marking this as solved so please do let us know if you need anything else!Ich habe den Fehler gefunden.
E164 war noch aktiviert.
Danke für die Hilfe!
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