Question 1

Is a valid VAT number enough to apply reverse charge?

Accepted Answer

No. A valid number is necessary but not sufficient. The buyer must also be a business established in a different EU member state from yours. If any of the three conditions fails, you charge your own domestic VAT.

Question 2

What does it mean when VIES does not answer?

Accepted Answer

It means unknown, not invalid. VIES forwards the question to the member state register, and those services go down. Treating an unanswered check as invalid is how businesses end up charging VAT on an exempt supply, or the reverse.

Question 3

Does VIES cover the United Kingdom?

Accepted Answer

No. Since Brexit VIES covers the EU member states plus Northern Ireland, which uses the XI prefix. For a UK VAT number use the HMRC service.

All three, or no reverse charge	The buyer must be a business, in a different EU member state from yours, with a VAT number that VIES confirms. Miss one and you charge your own domestic VAT. This is where it goes wrong most often: “they're an EU company” is not the test.
Unavailable ≠ invalid	VIES forwards the question to the member state, and those services go down. An unanswered check is unknown, not negative. Invoicing without VAT on the strength of a failed lookup is the expensive version of this mistake.
It expires in practice	A number valid today can be deregistered tomorrow. Tax authorities expect the check to be dated, which is why we store the date of the check and clear it whenever the number changes.
The name may be hidden	Some member states return the number's validity but not the company name. That is their choice, not a failed lookup.

EU VAT number checkFree. No account.

A valid number is necessary for reverse charge. It is not sufficient.