This option will only be activated if you have previously indicated that your account is a professional account (by clicking on the "I'm a professional" button)
To indicate your VAT number :
In this section, you will find a space to enter your Tax identification number in the "Company Information" section
Note: the section for entering your Tax identification number is permanently connected to the Europa.eu website, it will automatically recognize if your VAT number is active at that moment.
Example :