A very frequent issue that pop ups in our support department is the fact that users forgot to fill in VAT registration number on the customer before they are posting EC sales invoices / credit memos.

To avoid that these sales invoices should be booked without VAT registration number, it should be better if there is a check. This check can"t of course not being performed for all customers. But for the EU-customers these customers needs to be checked.

* Add to VAT business posting group - new boolean 'mandatory vat registration number'
* Change posting sales routines
- During the posting of a sales invoice it should be checked if the VAT business PG has the character 'mandatory VAT registration number'
- When mandatory, then the sales document could only be booked in case the customer has a VAT registration number filled in on the customer card.

Or maybe better : to be 100% sure if you may invoice with reverse charge, perform a check with the VAT VIES webservice to check if VAT registration number is still valid (also log the check in VAT log). If not valid > block to post invoice.