The following error emerges while registering a domain with the OpenProvider plug-in:
Error occurred during registration. Error: Can not create contact. Invalid vat number !.
Such behavior was classified as the software issue PBAS-29755 and was fixed in OBAS 4.5.5.
To resolve the issue, please upgrade to 4.5.5 as described in How to upgrade OBAS system to the latest available version.