Hey I work for a 3rd party retailer and we've been trying to figure out how to fix this problem that keeps popping up. We figured out a solution that has yet to fail in our trials so hopefully this works for you.
Go to the Google play store and search for the VoWiFi app made by Cast4TV. Open the app and follow the instructions on the screen. Enable the wifi calling from within the app and then again on your phone. After you enter in the emergency location info you are all set and you can delete the app.
Hope this helps!!! It worked for me and some customers all with our Samsung Galaxy S21 Ultras.
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