How can I link the 'buy' button on one of my forms to my other form with payment integration and other fields?

I would like my customer to click 'buy' and be taken to my payment form or another page with payment form on it.

There is already a guide to pass a value to a payment field either in the same form

http://www.jotform.com/help/275-How-to-pass-a-calculation-to-a-payment-field

or to a second form:

http://www.jotform.com/help/270-How-to-Pass-a-Calculated-Value-in-a-Paypal-Field-of-a-Second-Form

If you need a more elaborated help, do not hesitate to get back to us