Hi there,
It looks like VoWiFi is not yet unlocked on this phone. If you are a tech enthusiast, you might want to check this thread on XDA-developers out. It helps to unlock VoWiFi, but require getting root access to the phone.
https://www.xda-developers.com/enable-vol...
I'd personally prefer to wait until the function becomes available to the mainstream users.
Best regards,
Greg

The best thing to do is to contact our customer service directly at https://helpcenter.digitec.ch/hc.... Your request can then be examined individually.