I've tried implementing something like this but in the service industry. My solution didn't integrate into any POS system and relied on the staff to facilitate the distribution of awards by confirming reward payout amounts. The staff were the ones who ended up "killing" the idea (it's technically not completely dead yet) because they had no interest in informing customers of this program and didn't care for customers using cashback in the future (since they wouldn't be getting the same amount in tips).

Even if we aligned incentives better so they would receive some of the cashback (which is hard because the business owner would probably be against lowering margins any further and we were already low amounts in cashback), they didn't seem to care enough to learn how to sell/spend their Bitcoin.

My learning from this was that I overlooked the incentive requirements that needed to be present for everyone in the pipeline to enthusiastically participate, since service workers don't seem motivated enough to do anything "extra" for their jobs (even if these things were made to be part of their jobs by their boss).