Recently read that the money you receive from cash back credit cards are not taxed. I pay everything possible with a cash back credit card including my real estate tax. Have to watch Ultility companies. During the pandemic they only charged a very small fee but since have tripled it.If you use to purchase more items that would be business expenses it is no different than using a coupon or other discount from the seller.
If you use the voucher to purchase personal items it doesn't impact your business income. If they don't send you a 1099, IRS won't know you received these extra funds, but at same time they are not giving you cash or a check that you can do whatever you wish with, it is something you must use at their stores.