In order to get the patron discount at Kafka, you have to have bought some amount of stuffs from them before.
I'm not sure what the amount of stuffs are, but they trigger different discounts.
Currently I'm getting 15%. I've heard others say they get 10%.
It's tied to your account and just shows up in your basket.
Sometimes they send out codes which stack on the patron discount. Sometimes the code replaces the patron discount.
I think that PATRON code is dead.