Provide a better error message when VIES validation results in an invalid VAT number

When the provided VAT ID number is invalid according to the validation by the European Union's VAT Information Exchange System (VIES) through the SOAP service, we currently receive the following error message:

The VAT number could not be validated by the European VAT Database. Please go back and input a correct VAT.

This message could be improved:

• "the European VAT Database" is correctly called "the European Union's VAT Information Exchange System".
• "Please go back" should be removed since the user actually can't go back, but instead has to correct the VAT ID number on the current page.
• "input a correct VAT" means the amount of tax, but not the VAT ID number.