If this happens, please ensure that you have included the two-character country code at the beginning of your VAT number. For example, if your VAT number was GB1231231231, you would type GB1231231231, not 1231231231.
If you have done this, and you are still getting the invalid VAT number message, please verify your VAT number here:
We use an external service for VAT number validation, and the uptime, response time, and correct functioning of this service is something that we can not control directly.
If your VAT number is valid, the issue may may be that our third-party service is down for the moment, and it might work if you try making a purchase again, later in the day.
If your number is valid and you try again later, and it still doesn't work, please email firstname.lastname@example.org and let us know about the issue.
In the absolute worst case, if you have a valid VAT number and the service is rejecting it, and you have made sure you typed in the country code, then the best thing to do is to just not provide a VAT number, and buy the book or course, paying the VAT like any individual would.