VAT numbers need to be validated by your Tax authority, and some validation services aren't available 24/7. If you see an error at checkout, check the European Commission's VAT validation service opening times.
Another reason could be that your VAT number isn’t eligible for cross-border purchases. You can verify its eligibility through the European Commission's VAT number check.
Note: VAT numbers are only accepted for Pro Subscriptions. They cannot be used with Creator Subscriptions.