Mobile – Best way to dynamically add more fields to the form

I have a form so the user can issue an invoice, it is basically composed of comboboxes and 90% of the time the user will send the receipt with only one product, but rarely it will send with more than one, my question is whats the "best way" I can add a button or something so the user can add (and remove) more products to the receipt.

My current form: