Apache will not start, or a .htaccess took the site down.
cPanel and some DirectAdmin stacks still serve through Apache. apachectl configtest before a restart. The VPS stays yours.
The config, the handler, the rewrite
A bad include, a certificate path, a port already taken by NGINX. The error is in the config test. We do not restart a server that fails it.
A rewrite loop, a PHP handler the account no longer has, or a rule added by a plugin. We pull that file aside and confirm the vhost before rewriting the rule.
prefork with mod_php, or a proxy to PHP-FPM. Mixing them is how one account gets the wrong version. EasyApache on cPanel is the supported way to change that, not a hand edit.
If NGINX proxies to Apache, the 502 may be either
Hestia and some DirectAdmin setups do that. We check which process owns port 80 before editing the wrong vhost. Moving a site off Apache onto NGINX only is a planned change, not a troubleshooting step.
€55 an hour. Site down is emergency, if someone is free.
Minimum 1 hour. Emergency €95, subject to availability. Theme rewrites and plugin code are not part of an Apache repair.
Apache down after a .htaccess or an EasyApache change?
Tell us the panel and the error. No root password in the first message.