WHMCS is a web host billing automation and support system. It allows the web hosts to manage their billing automation and support system.
If you have migrated your WHMCS installation from one server to another server or if you have upgraded Apache/PHP software on your existing server, it is possible that you may face an issue due to misconfiguration or other changes in latest version.
Recently I faced an issue with WHMCS login problem for admin area as well as client area. It was not allowing to login unless you select “Remember me” option during login. Also, in admin area, it was not loading menu properly. This installation was recently migrated from old server to a new server.
After reviewing logs, we came to know that the issue was related to PHP session. PHP session was configured properly and it was working without any issue for other website. After careful investigation, we found that there was custom php.ini file present in WHMCS installation folder and it had custom path for PHP session. Since we moved to latest PHP 7.3 version on the new server, custom PHP session path was not accessible.
We immediately changed PHP session path in custom php.ini and everything started working properly. If you are facing similar issue, you can review your PHP session path setting in your PHP configuration. If it is incorrect path, you will need to fix it.