It’s not about the 20% that comes back to you, but, rather the membership you initially pay, which is not permissible.

You may buy and you may not buy. This is gambling.

Is Joining a Shopping Cash Back Program Permissible? (It works like, I pay fee to join and monthly membership fee and choose 10 stores that I want to do my usual shopping and nominate a Debit Card that I will be using for it and from the Purchases I will get 20% of the money I paid, paid back to me) is the 20% of the money that is coming back to me Halal?