I verry sorry for my english. This is no my first language and auto correction made a mess.
For clarity:
1. My network support VoLTE.
2. I'd tried use both SIM card slots.
3. Incoming calls are made by LTE (when blocking the network on LTE, there is no problem receiving calls)
3. SMS also (incoming and outgoing)
4. There are problems with APN for xcap
Something in the configuration is incorrect and APN config is missing. There are problems after adding it manualny. Problems with registration in this APN or all APNs when mvno type is valid.
Yes, I'm aware that the problems are the results od the lack operator support for this model.