Hello,
I go with my first installation in a shared hosting with Cpanel, SSH enable and Composer
My Cpanel system working with PHP 7.2 and not have any possibility to update the core by me and Flarum need 7.3 to working. In my Cpanel have a "multi PHP option" that its possible change the PHP subdomains I add to the panel.
The domain where I go to install Flarum change via "multi PHP option" to PHP 7.3 option but when go to install via composer have a error that said me: "the PHP 7.2 version is not compatible".
I contact with support and they said to go with this other option to run composer under PHP 7.3
ea-php73 /opt/cpanel/composer/bin/composer
This is working for me to install Flarum and extension without problem even though running PHP 7.2 in Cpanel core
Its possible that the address where is it installed composer change in other shared hosting.
Maybe its ok to add to guideline to install in shared hosting.
Sorry for my bad english.