David B easy, you buy 3 vouchers of 50, 100 or 500€ each, and they add one free. So, what I have done is to buy 3x 50€ vouchers, so I paid 150€ but got 200€. Then, on a second buy, I have put the F308 Standard which is 245€ on the cart. Then, when paying it, you can add, one by one, the vouchers. At the end, you need to pay 45€, so the real cost would be 195€
My extra trick is that, due to my work, I can buy VAT-less in Europe so, instead of 245€, the cost was 202,48€. So I only paid 2,48€ on last payment which, added to the 150€ of the 4 vouchers leave the 152,48€ real cost for me.
All in all, that is how vouchers work. Summing up, first you buy and pay for them, and later you buy anything you need, using them on the payment.
PS: sorry, I thought you had already bought it. So, yes @dore_m , I still have the speed record 😇