I have Gravity + PayPal addon set up on a site in order to manage workshop registration. User can select to attend one or more days...
In order to achieve this, I have set up a hidden product field at $0.10 and then added a required option field with checkbox select, so the user can select one day at (x) amount or 2 days at (x + x) amount.
The total shows up perfectly at the bottom of the form. When submit is clicked, however, the total amount is not passed to paypal.... just the product amount is. For some reason, the option amounts are dropped and not sent to PayPal..
So if a user selects Day 1 ($34.50), total shows $34.60 - submit is clicked and a payment of $.10 shows up on PayPal site.