Troubleshooting a Service Not Found Error on Domain Move
After updating to WHMCS 8.4.0, you may observe the following error when attempting to move a domain record to another client:
Service Not Found
Apply the 8.4.1 Maintenance Release via the Utilities > Update WHMCS page.
A hotfix has been created for WHMCS 8.4.0 only to correct this behavior: