Gift Voucher Guide Please

Hi there! can anyone help me on this? What I want is we will offer an incentive to the customer to buy us a machine by offering him a $5,000 voucher to be used for other products. I need to create a link so that the buying of other products with the $5,000 voucher is linked back to that customers proposal and not seen as a separate transaction. How will I do this? Is it discount coupon or gift certificate?

Thanks!

any help please? I am just confused with gift voucher and discount coupon. Is it possible to deduct the current purchase to the current balance? For example I bought a machine so I was given a code (still dont know if im going to use gift certificate or discount coupon). When I use this it will not be seen as a separate transaction and the amount I use (for example $15) will be deducted from the $5000 voucher.

Hope Im making sense.

TIA