When a payment is not applied, an account is not created or an email never arrives, WHMCS almost always recorded why. Knowing which log to open turns hours of guessing into a two-minute fix. This guide maps common problems to the right place.
Before you start
- Administrator access with permission to view logs.
- The client, invoice or service involved and the approximate time of the problem.
Start with System Health
Go to Utilities → System → System Health. It checks PHP version and extensions, cron status, file permissions, SSL, outdated modules, insecure settings and database issues, and rates each as OK, warning or danger. Fix red items first – a stopped cron or wrong system URL explains many other symptoms.
Which log for which problem
| Problem | Where to look |
|---|---|
| Account not created, suspended or upgraded on the server | Utilities → Logs → Module Log (enable logging first) |
| Customer paid but invoice still unpaid | Billing → Gateway Log |
| Email not received | Utilities → Logs → Email Message Log and the Activity Log for SMTP errors |
| Email to support not turned into a ticket | Utilities → Logs → Ticket Mail Import Log |
| Invoices or reminders not sent | Utilities → Automation Status |
| Who changed something | Utilities → Logs → Activity Log and Admin Log |
| Domain action failed | Module Log (registrar modules log there) |
Enable module debug logging
On the Module Log page, click Enable Debug Logging. WHMCS records every API request and response between WHMCS and servers or registrars. Reproduce the problem, read the response, then disable logging again – logs can include sensitive data and grow quickly.
Blank pages and "Oops" errors
- Temporarily enable Display Errors under Utilities → System → General Settings → Other (or set it in
configuration.phpwith$display_errors = true;if you cannot log in). - Reload the page to see the PHP error and the file causing it – often a third-party module or hook.
- Fix or disable the module (rename its folder), then turn display errors off.
The PHP error log of your hosting account (for example error_log in the WHMCS folder on cPanel) also records these errors.
Clean up
Utilities → System → System Cleanup lets you empty the template cache (fixes theme changes not appearing), prune old logs and remove old attachments. Clearing the template cache is safe and often the first step after editing templates.
Getting help
When asking WHMCS support or a developer, include the WHMCS version (shown in the admin footer), PHP version, the exact error text and the relevant log lines. For server-side issues with your MdmHost hosting, open a ticket with the same details.
Troubleshooting checklist
- Is the cron running? See cron troubleshooting.
- Is the WHMCS System URL correct and on HTTPS?
- Did a recent update or new module coincide with the problem?
- Is the server time and time zone correct?