When goods are sold and delivered to another EU VAT registered business the reverse charge applies. To zero-rate the invoice you must make sure that the customer’s VAT number is valid. The number can be verified on the European online VIES system.
When the Reverse Charge applies, the recipient of the goods makes the declaration of both their purchase (input VAT) and the supplier’s sale (output VAT) in their VAT return. In this way, the two entries cancel each other on the VAT return.