How would you get the suppliers to adopt this? Usually a lot of protocol adoption (outside of tech, but often in tech as well) is top down and mandated.

Yes you have right, usually protocol arrives from the top. here the supplier can receive an email with the pharmacy's command until he will build his agent. I have made an email bridge with the protocol to help them adopt this language. So we need only one pharmacy to begin, and that's what's I am doing in my own one. The supplier can plug his ERP when he will be ready.