TatukGIS must charge the Poland value added tax (VAT) - presently 23% - to buyers located within the European Union (EU), unless the buyer provides a valid European Union VAT number. Sometimes a buyer has a VAT number issued by its EU country, but the VAT number has not been registered with the EU VAT administration for use for cross border transactions within the EU.
The validity of an EU VAT number can be confirmed using the service at EU web site: http://ec.europa.eu/taxation_customs/vies/
The procedure to register a VAT number with the EU, or otherwise fix a problem with an EU VAT number registration, is for the tax payer to take up the matter with its local tax administration.