I am upgrading a server from Debian 9 (stretch) to Debian 10 (buster), and am aware (and intend) that this results in PHP being upgraded from PHP 7.0 to PHP 7.3.
php -v does indeed show that PHP 7.3 is installed, but when trying to login to the web application running on the server, I get a (vague) error message, and, when I create a test page to run phpinfo, it shows that Apache still seems to be running PHP 7.0.
I had expected that Apache would switch to using PHP 7.3 as part of the OS upgrade. What do I need to do to make Apache now use PHP 7.3?