Troubleshoot and resolve Oops! Access Denied - Forbidden errors while logging in to WHMCS. Troubleshoot and resolve Oops! You have sent too many requests errors while logging in to WHMCS. Troubleshoot and resolve `PHP session storage is not writeable. For help, contact your system administrator.` errors when logging in to the WHMCS Admin Area. Troubleshoot and resolve issues with sessions not being removed. Troubleshoot and resolve `OAuth authorization request denied due to unexpected active login session for 'Closed' User ID` errors. Troubleshoot and resolve `Single Sign-On authentication denied for 'Closed' User ID` errors when attempting to use WHMCS single sign-on. Troubleshoot and resolve `Single Sign-On authentication denied per configuration for User ID` errors when single sign-on is disabled. Troubleshoot and resolve `Unable to authenticate with Single Sign-On token for User ID` errors during WHMCS single sign-on. Before you can enable two-factor authentication (2FA) for users or admins, you must enable it globally for your WHMCS installation. Configure two-factor authentication (2FA) for Admin Area logins. 2FA enhances security by adding a second step to the login process. Configure two-factor authentication (2FA) for Client Area logins. 2FA enhances security by adding a second step to the login process. You can restore access to the Admin Area or Client Area after the loss of a two-factor authentication (2FA) device and backup code. If users or admins lose their two-factor authentication (2FA) device, they can regain access to WHMCS using their 2FA backup code. After you enable two-factor authentication (2FA), you can require users and admins to configure it the next time that they log in to WHMCS. Facebook® Sign-In Integrations let your customers register, sign in, and connect with your WHMCS installation. Google® Sign-In Integrations let your customers register, sign in, and connect with your WHMCS installation. Twitter™ Sign-In Integrations let your customers register, sign in, and connect with your WHMCS installation.