HTTP GET with request body RETROFIT

This error also occurs when API required @POST and you are using @GET

To send data along with your Get Request you can do the following:

//sending data as a url parameter
@GET("/group/{id}/users")
List<User> groupList(@Path("id") int groupId);

as said in this SO answer, Server semantics for GET, however, are restricted such that a body, if any, has no semantic meaning to the request- Roy Fielding.

The definition of GET as explained here in this answer explains that a body isn't supposed to mean anything, so Retrofit doesn't allow you to add a body. That said, it is not true that a server HAS to follow this format. It's entirely possible for a server to have a GET endpoint that not only takes, but REQUIRES a body. It would be "bad" architecture, but it seems a bit silly for Retrofit to limit what the library can do unnecessarily.

Furthermore, the various HTTP methods have different definitions for what they are SUPPOSED to do. For example a GET gets information, a POST creates a new entry/object by providing information to the server, a PUT updates an existing entry/object etc. The problem is, the easiest way to pass complex data to the server, especially when using retrofit, is by using JSON. So the ideal way to GET information from the server while providing a complex filter would be to send a JSON body along with the GET request. Unfortunately, there is no HTTP request method that allows for this under the spec.