If you own a business and your company is registered in one of the European Union countries then you have a valid VAT number which you can add to your receipts via your admin panel.
Go to the Cogwheel Icon > Settings > Billing > Account and you will see a section called VAT SETTINGS. Select your country and add your VAT number. To make sure that your VAT number is valid visit VIES VAT number validation.
A VAT number has the following structure: Country prefix + characters (varies from country to country. E.g. Sweden: SE+12 digits → SE999999999999