The website will not load or displays a 500 error. An error similar to one of the following will be in the PHP error log.
PHP Fatal error: Unknown: Failed opening required '/path/to/missing/file.php' (include_path='.:/opt/alt/php73/usr/share/pear') in Unknown on line 0
PHP Fatal error: require_once(): Failed opening required '/path/to/missing/file.php' (include_path='.:/opt/cpanel/ea-php56/root/usr/share/pear') in /path/to/calling/file.php on line 1375
The error occurs when a file required by the site is missing or in a location other than the one specified in the calling file.
Your developer should determine if the missing file is needed or not. If the missing file is needed, upload a copy of the missing file or correct the path to the missing file in the calling file. If the missing file is not needed, remove references to the missing file from the calling file.
Please note that if the error message contains "in Unknown on line 0," the missing file is specified in the php.ini file located in the site's document root or the account's home folder.