What to return if the object does not exist?

Question

API

There is an API:
/users/{id}
/groups/{id}/add?categiry={categiry_id}

What result should be returned if the given {id} does not exist?
What result should be returned if the given group category {categiry_id} does not exist?
What result should be returned if the given {id} or the given group category {categiry_id} does not exist?

Answer 1

statuses - select the appropriate status and return it in the response with a message, you can make a list of constants and some kind of dock with their description, or you can simply textually tell what the problem is
. If there is no suitable status, then no one bothers to add your own (for example, in laravel 419 is actively used because it is not reserved)