For a successful RESTful HTTP request, we can return an object that is serialized.
But in case of an error, for example when a resource is not found (404), should this return a HTTP response with error code 404, or can it alternatively return an object which has a custom error information in it?
...for example when a resource is not found (404), should this return a HTTP response with error code 404, or can it alternatively return an object which has a custom error information in it?
You can do both.
A 404 is a resource not found and your response status code should be 404. If you want to give additional information or have a special error object with particular codes in it then return that too as part of the body.
Also have a look at this post: REST API error return good practices
