API First Design Approach - What Are Your Thoughts?

The first step would be to define your domain models. And then after that, you're going to be designing how do you interact with the API. That's very efficient because that doesn't require any coding. It can be done by a product owner and things like that. All right. So I've been reading a lot about this API first approach. How does it become that first class citizen? Anyone of you can answer?