First you have to add the new customer to your customer list. You will need to fill in their data manually, due to them not being a Belgian company.If you want to send a VAT reverse charge invoice, you must be sure your contractor is an active VAT payer and all products and services must have a 0% VAT rate. You can check the list of VAT payers on the European Commission website. 

The headline “Reverse Charge” will be automatically added to the invoice when you issue it to the customer.