I'm hoping someone has dealt with this before.

I am trying to do this:

Form1 -> paypal -> Form2 (follow up form)

Form2 is suppose to use the invoice id from Form1. Does anyone know if there is a way to transfer the invoice id from form2 -> form2?

And what about using a cookie? I've found using a session isn't working out, and I know I can use a cookie, but I'm a little nervous about security.