Thank you for posting, @j-fomiatti.
Recording two-part payment in one invoice is easy and I'm here to help you how.
Receive the payment as usual on the invoice. On the Receive Payment screen, enter the first amount received and the payment date. I've attached a screenshot for my partial payment sample.
Next, receive the payment again for the partially paid invoice and enter the second amount received and its payment date.
That should do it. For other related articles about invoices and partial payments, you can also check the following links below.
Set up and send progress invoices in QuickBooks Online
Set up and use the Projects feature
Fill me in if you have other questions about your invoice transactions. I'll be here to help.