It seesm this is because GB left the EU.
Currently there are no plans to add an automated lookup for UK. And no plans to localize this feature to use local service endpoints and implementations.
There is an idea for the UK one with a fair amount of votes.
We are going to spend some time investigating if there are better services out there (that has a cost) that we could integrate to, that could provide a higher level of data. Like more structured addresses, so we could realize the original benefit of our feature, which was intended to pull in address and company name, in addition to validating the VAT Reg. No.
But no commitments at this point. Pure research.
Of course you should keep the VAT Reg. Validation enabled for other EU countries, but not for GB for now.
If you lookup the country/region code GB … is that still marked as “EU Country”?
If this is the case, then please set this to "false" for GB.
Then the error shoudl not appear anymore