General errors can occur in many places throughout WHMCS, and can be due to many different problems. However, fixing them is often simple. Each addon module has specific errors that you might encounter. Authentication issues may include inability to log in, unexpected logouts, or errors while using other authentication methods. We support many different ways to customize your WHMCS installation, all of which have their own troubleshooting needs. When you sell domains, issues with domain availability checks, registration, or renewals can cause serious problems. When you install WHMCS on a server, make sure to watch for errors both during and after the installation process. Issues with invoices and invoice generation can be due to many causes, some of which may not be obvious at first. You might see license-related errors if you cannot connect to the WHMCS license server or there is a misconfiguration in your system. If you experience problems with MarketConnect landing pages, promotions, or provisioning, it may be due to misconfigurations or other issues. If you experience problems with orders or fraud checks, it may be due to misconfigurations or other issues. Make sure to troubleshoot and resolve any issues with payment gateways, payments, currencies, or related features as soon as possible. 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. You may experience problems while configuring products for sale, during the purchase process, or when managing individual clients' purchased services. Some provisioning and server-related issues are due to misconfiguration in your WHMCS installation, while others may be due to networking issues or other server-side problems. You will see SSL-related errors if the SSL certificate for your WHMCS installation is missing, misconfigured, or out-of-date, or if there are connection issues. Problems with your system email can prevent you from sending email to clients or connecting to your mail provider. Issues in the Client Area or your online store can hurt customers' ability to purchase your products or access their purchased services. WHMCS uses a MySQL® database to store all of your business data, including client and financial records. Problems in the support ticket system and its related features can prevent email replies from importing properly and cause other disruptions. If the system cron configuration is incorrect or it encounters problems when running, you may see problems with automation throughout WHMCS.