How I understood that was that for example you sell shoe laces and want to give discounts to people who bought sneakers of brand x - but you don’t have any rel

How I understood that was that for example you sell shoe laces and want to give discounts to people who bought sneakers of brand x - but you don’t have any relation to the shoe seller. So receipt in pdf can be faked and they provide a solution so that buyer can prove they bought x and can claim your discount. But still rather contrived.