My account was created in switzerland. When i try to make a call from germany to switzerland there is always an error accuring (potentiellen Risiko von unberechtigter Verwendung") asking me for entering three spoken digets. Doing this it says there was no recognition of the digets. How can I prevent geofencing ?
Try speaking with your service provider, eventually they can whitelist you.
Otherwise you might need to use a VPN service. However, keep in mind that not all VPN services allow VoIP or have proper configuration.