Using Zapier, create an invoice in Keap (Infusionsoft?)

I will use the API if needed, i just really need to make an order, for an unspecified amount, and have the order saved in Keap. i need to automate this process.

Originally, i thought i could use the API to make orders and set the amount of the order when making an API call, but i cannot, as Keap has very strict policy of forcing you to sell products, and the products must have a set price.

my “workaround” idea is to make invoices for the variable amount, and then immediately make those invoices paid, and save the order/invoice, which should then have the correct order amount.