Hi, Attilio.

Yes, the PC or Web browser version of your QuickBooks Online allows you to add attachments when accessing invoices. In the mobile app, we can only add attachments to an expense.

When using the mobile app, there is no direct option to add your attachments for invoices. However, we can upload the file to your computer, log in to QuickBooks Online web browser, and open the invoice to add attachments. 

Here's how:

1. Once you have uploaded your files to your computer, open your QuickBooks account in the web browser.
2. Once logged in, head to the Plus Create and click the Invoice option.
   
3. Enter the necessary details.
4. Scroll down and click Add attachments.
   
5. Once done, Save and close.

You can view this article to check the transactions that support attachments: Add or delete attachments.

If you need to brainstorm or talk about attachments, feel free to reach out again.