This is how we do it-

1. Backend and frontend devs would do a technical discussion and come up with the final request and response structure.
2. Now the backend dev would start working on the APIs.
3. At the same time, frontend dev would use json-server to mock the decided API response and will develop accordingly, if the design is ready. If not then they will have to wait for that to finalize.
4. Once both sides are ready, they would sit together and see if the final integration is working as expected.

Usually, it's a very smooth process. Both devs are in sync and if any response, request change is required, then they would discuss and work accordingly.