As an agent, how to I invoice a supplier on behalf of my principal? The invoice should look like it's from the principal (e.g. their name, address, VAT number) not me.

Welcome to the Community, Julia. I'll walk you through the steps to invoice the supplier on behalf of your principal.

Since this transaction is for your supplier, you'll want to create a Bill. Then, we can utilize the Memo field from there. This is to add more details so you can easily track what the transaction is for, such as (e.g., their name, address, and VAT number).

To create one, here's how: 

1. Click + New and select Bill.
2. From there, choose a Supplier.
3. Enter the necessary information.
4. On the bottom left of the page, enter the additional information from your principal from the Memo field.
5. Click Save and Close.
   
   
   

To help you more about tracking bills and recording the payments, please refer to this article for a more detailed process: Enter and manage bills and bill payments in QuickBooks Online.

If you're also paying on behalf of the principal, this guide can help you record the transaction: Enter billable expenses.

I'll be glad to help if you have any other transactions related to bills or expenses. Have a good one.