Responsibilities of a back-end developer when building a RESTful API?

Question

API

I ask for help in clarifying the issue. Tell a beginner about the tasks of a back-end developer when building a RESTful API. His area of ​​responsibility. It is clear that the more experience and practice is good, but I want to know the minimum for the back-end and where the very watershed and the task of the front-end goes further. Do I understand correctly that, in fact, my main task when building is to write code so that when making requests to the server, the server returns information in the required format in accordance with the logic that is designed, in practice, you enter the address in the browser and bare json flies out to you.
It is clear that there is also access to the API, authorization, authentication, but we do not take this into account.