I think payments could be done easily if you used a credit system where people bought credits which were stored in your own database… then chips were used to debit the credits. They could then top-up credits using some external method like paypal or stripe.
How about post your project updates here! I’d love to follow along and give tips… learn about how you converted your vending machine, etc. I can probably even donate some implants to the cause… or maybe you guys could arrange a “chipping party” for the space?