Go to your order:
From the project: Go to the Billing tab of your project, then click on the relevant Order card
From the Billing Module: Type Purchase Order > click on the relevant Order card
For the IC VAT number (intra-community VAT) to appear on your invoices, you need to scroll down the page to the PDF Configuration of your invoices, then check "Display the client's IC VAT".
Then, save!
N.B.: The IC VAT number of your client must be entered in their Information card: