WHMCS runs on PHP code and requires several PHP extensions in order to function normally. If there is a problem with PHP on your server, you will experience problems in many areas of WHMCS.
Troubleshoot and resolve Allowed memory size of xxxxx bytes exhausted errors.
Troubleshoot and resolve ExceptionLoggingTrait Class Not Found errors.
Troubleshoot and resolve InvalidArgumentException: Data missing errors.
Troubleshoot and resolve Laminas Class Not Found errors.
Troubleshoot and resolve Legacy Smarty Tags errors.
WHMCS may return PHP errors and exceptions if errors occur.