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.
For successful installation, updates, and operation, your system must meet the minimum system requirements for your WHMCS version.
ionCube Loader® is a PHP extension that allows decoding and encoding of WHMCS files. Make sure your system uses the correct version.
Troubleshoot and resolve Allowed memory size of xxxxx bytes exhausted errors.
You can add PHP code to your custom templates.
Troubleshoot and resolve ExceptionLoggingTrait Class Not Found errors.
Troubleshoot and resolve InvalidArgumentException: Data missing errors.