Symptoms

When trying to register a domain or when creating a domain handle, the following error is being thrown:

Invalid suffix field!

Cause

"Address line 2" of WHMCS contact information tends to be mapped to the "Suffix" field of the createCustomerRequest API call.
Openprovider API validates the suffix field and does not allow the comma character (,) in it.

Resolution

This is a software issue of older versions of the WHMCS Registrar module. Please update to the new version available here.

Please suggest customer simplifying his Address Line 2 field, without the comma ",".