Troubleshoot and resolve Error detail URL may not contain a query string. errors.
Troubleshoot and resolve a POP3 cron not running emails and WHMCS Pop Cron Did Not Run errors.
Troubleshoot and resolve Error: read failed - connection closed? errors.
Troubleshoot and resolve Error: the single id was not found in response errors.
Troubleshoot and resolve Call to undefined method getRawHeader() errors.
Troubleshoot and resolve The sender's email address is not registered. (WHMCS 8.4 and later) or Unregistered Email Address (WHMCS 8.3 and earlier) errors.