I'm trying to buy with the offer you have today but it says my VAT number is invalid. I've already open a ticket but it can take 1 day to get it solved and I guess the ofer is only for today. Is there anything you can do to speed up the ticket?
We use the VIES website to validate these numbers (http://ec.europa.eu/taxation_customs/vies/) so you will need to make sure your number validates there to work on our site. They have an FAQ page to deal any problems.
The most common error though is that a space is needed between the country code and the number for it to work.
The service seems to be now working for German VAT numbers so may have been a temporary issue on the VIES site.
When entering a VAT number on the Sparkol checkout page ensure that you enter a space after the 2 letter country code.