Hello. I am a physician. I am creating a store in which I sell both supplements and prescription products. I am offering consultations (doctor apppointments) in which if a patient is qualified, they can receive a prescription for a medical product. Shopify has denied me use of their payment system (for medical services) and I do not know what to use as a payment gateway now. I am not only selling prescription products but also regular products such as supplements. I am wanting set up a payment gateway that works in two ways. This is due to the fact that the products that require a prescription can only be sold to those patients who have a prescription for the product. I can only allow for patients who have a prescription to be able to purchase prescription products. But I will also sell supplements, which anyone can purchase. I am trying to have it set up where, once a patient receives a prescription, only then they can purchase that specific medical product. And only at "x'' amount of quantities. How can I go about doing this? And what payment gateway should I use? Thanks.