I have a form (form ID 4) where I used a "User Defined Price" Product field (field ID 4), to collect the amount that the user is going to pay. I also have a Single Line Text field (field ID 10) that the user inputs their invoice number (invoice was mailed out to them).
Since PayPal has nothing available to send over a reference or invoice number, I want to append 'Inv #' and the input from field 10, to the label of field 4, and send that to PayPal.
I did some research, and know what I need to use gform_pre_submission_filter, but I don't know where to start to make this work. (I saw this http://www.gravityhelp.com/forums/topic/paypal-for-invoices-user-defined-price, but it is not what I need because it always updates 'invoice 123', and I can't make it work).
How is this done (hi David Smith lol)?
Help is greatly appreciated!!