Not sure it competes with Amazon/Walmart, those would probably end up the places where the agent would purchase from. They're not becoming a marketplace for merchants, this is just a protocol so that the AI agent can place a purchase on any site that supports it.

Also, OpenAI is not handling the transaction, Stripe is, but it doesn't have to be Stripe, just that Stripe co-developed the protocol with OpenAI and is first to have it available.