Why my HTC ONe M9 won't connect wifi calling when wifi network is just fine for all other apps?

[Android Central Question]

When I turn on Wifi calling, it will turn off almost immediately. I've tried clearing the cache, and other switches, all to no avail. I had even reformated 10 days ago related to getting locked out. Then I had trouble connecting to mobile data last week when out of town. The network connection, apps, and browsing all work fine.

 

[mustang7757]

When I turn on Wifi calling, it will turn off almost immediately. I've tried clearing the cache, and other switches, all to no avail. I had even reformated 10 days ago related to getting locked out. Then I had trouble connecting to mobile data last week when out of town. The network connection, apps, and browsing all work fine.

Hi , if you can register a account here , me or other members be happy to assist.

I'll provide a link to register so you can communicate here.
https://forums.androidcentral.com/ask-question/409154-join-android-central-community.html

 

[Rukbat]

Is it a carrier-branded phone, or an unlocked phone (or a carrier-branded phone used on one of the carrier's MVNOs)?

Most phones won't work on WiFi calling, unless you're using the carrier itself, and the phone is carrier-branded. (WiFi calling is implemented differently by different carriers, so most phones have to have firmware specifically for that phone, and many MVNOs don't do WiFi calling for the carrier they use.)