I have problems making WiFi Calls on my Samsung Galaxy S9+
If you can't use WiFi Calling, there may be several causes of the problem.
Press Phone.
Press the menu icon.
Press Settings.
Press the indicator next to 'WiFi Calling' to turn the function on or off.
When WiFi Calling is active, the WiFi Calling icon is displayed.
Press the Home key to return to the home screen.
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Slide your finger downwards starting from the top of the screen.
Press the settings icon.
Press Software update.
Press Download updates manually. If a new software version is available, it's displayed. Follow the instructions on the screen to update the phone software.
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Press and hold On/Off.
Simultaneously, press and hold the lower part of the Volume key until your phone restarts.