D120 - SIP invite with no response when making international calls (prefix 00)

I have a D120 which I can use with local calls but when dialing international numbers (00 or + prefix) the SIP invite does not get an answer. I see in the SIP trace that the request is correct. I have tried with other devices or soft phones (e.g. Zoiper) and the calls work. I don´t have any call plan set up in my Snom phone. Any ideas what the issue might be?

The provider is netelip, and, as I said, calls work when using other devices.