Find your NextCloud “config.php” file.

cd /var/www/[. . . path . . . ]/nextcloud/config/ 

List files in the config directory:

ls

config.php

Use Vim or Nano to edit the config.php file.

sudo vim config.php

Before the line containing:

 'maintenance' => 'false',

Insert the following line:

'default_phone_region' => 'US',

Near the end of the config.php file should look like this:

  'default_phone_region' => 'US',
  'maintenance' => false,
);

Save the vim or nano edits/changes to the config.php file and restart apache2

sudo systemctl restart apache2