Guides & Tutorials
Browse our easy to follow guides and tutorials that demonstrate how to use WHMCS and resolve common problems.
Topics
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Common Errors 24
- Troubleshooting CURL Error: 56 - OpenSSL SSL_read: Success error
- Troubleshooting ionCube Errors
- Troubleshooting Question Marks in PDF Invoices and Quotes
- Troubleshooting an "Allowed memory size exhausted" Error
- Troubleshooting Impossible to create the root directory Errors
- Troubleshooting a 404 Page Not Found Error
- Troubleshooting reCAPTCHA Invalid Domain for Site Key
- Troubleshooting CURL Error: 56 - OpenSSL SSL_read unexpected eof while reading
- Troubleshooting an InvalidArgumentException: Data missing in Carbon.php:425 Error
- An error occurred while communicating with the server. Please try again
- Troubleshooting a Critical Error - Could not connect to the database Error
- Troubleshooting an Argument 1 passed ... must be an instance of PDOStatement Error
- Troubleshooting a Failed Opening Required file Error
- Troubleshooting a Duplicate entry '0' for key 'PRIMARY' Error
- Troubleshooting an Access Denied - Forbidden Error
- Troubleshooting an TypeError: Argument 1 passed to Carbon\CarbonInterval::setLocalTranslator() Error
- Troubleshooting a The template could not be found Error
- Troubleshooting a You are currently accessing the admin area using an insecure connection Notice
- Troubleshooting an InvalidArgumentException: Query string must not include a URI fragment Error
- Troubleshooting Backup Errors
- Troubleshooting a The file /path/to/whmcs/index.php is corrupted. Error
- Time-Based Tokens QR Code Image is Broken
- Troubleshooting Dataset must be an array in /vendor/whmcs/whmcs-foundation/lib/TableQuery.php
- Troubleshoot Duo Security Login Failures
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Advanced 9
- How to Resolve A Certificate Authority Verified SSL Certificate Was Not Detected on example.com
- Troubleshooting Unsupported Protocol Errors (TLS Support)
- Troubleshooting an Order Not Found...Exiting... Error
- Troubleshooting Server IP Address Appearing in Client Logs
- Resolving a Base table or view not found Error
- Troubleshooting Frequent Logouts
- Sending Failed. Please see documentation SendEmail API response
- Troubleshooting Admin Directory Errors
- TypeError: Return value of WHMCS\File::guessFileExtension() must be of the type string
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Billing Troubleshooting 6
- Troubleshooting Domain Invoice Generation
- Integrity constraint violation: 1062 Duplicate entry '2147483647' for key 'tblinvoices.PRIMARY' Errors
- Troubleshooting Service Invoice Generation
- Troubleshooting Unexpected Service Suspensions
- Troubleshooting Unexpected Service Terminations
- Troubleshooting Domain Invoice Cancellation
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Email Troubleshooting 10
- Troubleshooting Email Sending Problems for WHMCS 7.x
- Troubleshooting Welcome Email Sending Issues
- Troubleshooting Email Sending Problems
- Troubleshooting Administrators Not Receiving Support Ticket Notification Emails
- Connection unsuccessful. Please close this window and try again with Microsoft
- URL may not contain a query string with Microsoft
- SMTP connect() failed Error with External SMTP Mail Providers
- Troubleshooting a Cannot connect to host (php_network_getaddresses: getaddrinfo failed: Name or service not known) Error
- Call to undefined function PHPMailer\PHPMailer\escapeshellarg() Errors
- Troubleshooting a last request failed: [AUTH] Username and password not accepted error with Gmail
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Simple 10
- Troubleshooting a Blank Page/Oops Error Message
- Troubleshooting Login Problems
- Troubleshooting Warning Messages
- How to refresh admin dashboard widgets
- Resolving Attention Items on the System Health Status Page
- Resolving Warnings on the System Health Status Page
- Troubleshooting a Redirect Loop
- Troubleshooting Twitter Sign-In Integrations
- Troubleshooting Facebook App Review Requests
- Is WHMCS Compatible with ionCube Loader® 13?
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Troubleshooting Customizations 7
- Restoring Default Email Templates
- Troubleshooting TCPDF ERROR: [Image] Unable to get the size of the image
- Troubleshooting Empty Page Contents
- Replacing Legacy Smarty Tags with Hooks
- Eliminating Legacy Smarty Tags in WHMCS 8.7+
- Troubleshooting and Debugging WHMCS API Calls
- Troubleshooting & Debugging Hooks
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Troubleshooting Clients, Services, and Domains 6
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Troubleshooting Cron Automation 14
- Verify Whether Your System Cron is Completing Successfully
- Verify That Your System Cron is Being Invoked
- Troubleshooting the Cron Not Completing
- Advanced Cron Troubleshooting
- Advanced Cron Troubleshooting - Intermittent Issues
- Resolve cron has run within the last 24 hours message
- Resolving a Cron Invocation Frequency Warning
- Resolving a Daily Cron Run Warning
- Identifying the php.ini used for in command line/cron engine
- Identifying the timezone used in command line/cron engine
- Cron stuck on Executing System Queue step
- Maximum execution time of 300 seconds exceeded in /path/to/whmcs/vendor/tecnickcom/tcpdf/tcpdf.php
- Cron Halts on Tenant Usage Metrics
- No input file specified
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Troubleshooting Localization 2
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Troubleshooting Payments and Currencies 12
- Troubleshooting Client Details Display Issues on Invoices
- Troubleshooting sslv3 alert handshake failure and tlsv1 alert protocol version Errors
- Why did a service Next Due Date move forward several billing cycles?
- Troubleshooting users logged out when downloading invoices
- Troubleshooting a This Payment Solution module could not be loaded Error
- Troubleshooting a Remote Transaction Failure Please Contact Support Error
- PayPal Checkout SSL Requirement
- Troubleshooting a Module Not Found Error
- Understanding PayPal Checkout Subscription Log Entries
- Troubleshooting Empty Invoices and Duplicated Reminder Emails
- Troubleshooting Chrome Browser Crashes with 2CheckOut Inline Checkout
- Stripe and Reserve Bank of India (RBI) Regulation Warnings
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Troubleshooting Provisioning and Module Issues 13
- Product attribute Package Name XXX Not Found on Server
- Troubleshooting An Unknown Error Occurred
- Troubleshooting a No nameservers are defined for the server this domain is assigned to Error
- Troubleshooting Status Monitoring
- Troubleshooting at Module Command Error Failed to load module "WpToolkitCli" Error
- TypeError: Argument 3 passed to WHMCS\Domains\AdditionalFields::processFieldOverrides() must be of the type array
- Invalid value "paper_lantern" for the "cpmod" setting
- Troubleshooting a _getSSORedirectUrl() must be of the type string, null given Error
- Troubleshooting Module Command Errors
- Troubleshooting Product Provisioning Problems
- Troubleshooting Domain Provisioning Problems
- Troubleshooting Domain Renewal Problems
- Migrating to PayPal Payments
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Troubleshooting Support Tools 14
- Troubleshooting Email Piping Problems
- Troubleshooting Email Piping Problems - Advanced
- WHMCS Pop Cron Did Not Run Email
- Troubleshooting an Argument 7 passed to processPoppedTicket() Error
- Troubleshooting a cannot select INBOX, is this a valid transport? Error
- Troubleshooting a Logon failure: unknown user name or bad password Error
- Troubleshooting a Cannot connect to host (php_network_getaddresses: getaddrinfo failed: Name or service not known) Error
- Troubleshooting a TypeError: Return value of convertIniSize() must be of the type int Error
- Bad Request Error Importing Microsoft® Email
- POP3 read failed - connection closed? Errors
- the single id was not found in response Errors
- Troubleshooting a General error: 3988 Conversion from collation utf8mb3_unicode_ci into latin1_swedish_ci impossible for parameter Error
- Inconsistent Timestamps in Support Ticket Messages
- Ticket Creation Failed: The system could not generate a ticket number because it reached the maximum number of attempts.
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Updates 17
- Automatic Update Failed: Identifying the problem
- Troubleshooting a Check for Updates Failed Error
- Troubleshooting an Update Message Validation Issue Error
- Troubleshooting a File could not be downloaded error
- Troubleshooting a Blank Admin Dashboard After Updating
- Resolving a Down for Maintenance Message
- Troubleshooting A "PHP Fatal error: Class not found" Error
- Resolving MySQL Error Code 1146 - Base table or view not found
- Troubleshooting A Failed to remove legacy modules Error
- Troubleshooting A fatal error occurred while fetching the update Error
- Troubleshooting a Down for Maintenance Error while Updating WHMCS
- Troubleshooting an Apply update dry-run permission issues Error
- Resolving MySQL Error Code 1142 - Command denied to user
- Troubleshooting a cURL error 28: Operation timed out Error
- Troubleshooting Failed Communication with Update Server Error
- How to Resolve Unable to Perform Automatic Updates
- Troubleshooting Problems Accepting EULA After Update
Other Resources
- Support Announcements
- General Topics
- Updating WHMCS
- Third-Party Tutorials
- Admins and Permissions
- Clients and Services
- Customization
- Installing WHMCS
- Localization
- MarketConnect
- Order Forms
- Payments and Currency
- Provisioning Modules
- Security
- Setup and Configuration
- Support Tools
- System Settings
- Troubleshooting
- Other
- Cron/Automation
- 8.12 Update
- 8.13 Update