Wouldn't it make sense if you get a message after paying at the self-checkout whether you want to receive the vouchers (2x Cummulus or the personalized vouchers) on paper or only digitally?
1. paper saved
2. waste saved (I personally usually dispose of these slips of paper on site in the existing "slot" which is apparently very difficult to empty, as I observed today)
And if this goes well, it could also be extended to the attended checkouts.
Greetings from the Rhine Valley.