It's a new space, everyone is coming up with their own protocols. It's really no different than Stripe offering an API so you can use them as a payment provider. You need to implement this API on your website so ChatGPT can allow users to buy stuff from you.

You need some amount of strictness in the API here, LLMs are not actually sentient. You could say that this is a failure on OpenAI's part in comparison to their marketing, sure.