If when entering login details you are redirected back to the login screen without any error, this indicates an issue with PHP sessions on your server.

This can be confirmed by checking Remember Me on the login page:

If you are logged in with this option checked, it confirms there is a problem with PHP sessions. Common things to check for include:

• The configured session tmp path not being writable.
• The configured session tmp path being full.
• A misconfiguration of proxy or CDN in front of your webserver

This is a PHP or environment configuration-level issue. Shared or reseller users will require the assistance of their hosting providers.

WHMCS will identify the common causes of PHP session problems and display them at Configuration > System Health.

For more information, see PHP Session Support.

If your webserver is behind a proxy, load-balancer or CDN, a misconfiguration could be causing the session problem.

Refer to the Trusted Proxy Settings documentation for guidance configuring WHMCS for use with proxies, load-balancers and CDNs.

As a security measure, WHMCS evaluates a visitor's IP address against the expected value. This can be disabled temporarily:

1. Navigate to Configuration > System Settings > General Settings > Security tab
2. Check the Disable Session IP Check option
3. Click Save Changes

Database session data is stored in flat files at the location defined by the PHP configuration. Storing session data in a MySQL database is desirable in some environment configurations and can workaround problems with file storage.

Refer to Sessions Documentation page for more information and instructions.