Android Retrofit | POST a shared object for server and client, inside a custom object to the server (send json to server)

I was wondering how could I go about sending a custom object to my API using retrofit, something like this:

@POST("SubmitGeneralRequest")
Call<ResponseBody> sendGeneralRequest(@Body GeneralRequestRetrofit simpleRequest);

For the custom object is something like this:

public class GeneralRequestRetrofit {

    private String loginDomain;

    private Map<String, String> authParams;

    private String requestCode;

    private Resource resource;
    //Resource is a class that be shared with server-side and client-side (Android)

    public GeneralRequestRetrofit() {
    }

    public String getLoginDomain() {
        return this.loginDomain;
    }

    public void setLoginDomain(String loginDomain) {
        this.loginDomain = loginDomain;
    }

    public Map<String, String> getAuthParams() {
        return this.authParams;
    }

    public void setAuthParams(Map<String, String> authParams) {
        this.authParams = authParams;
    }

    public String getRequestCode() {
        return this.requestCode;
    }

    public void setRequestCode(String requestCode) {
        this.requestCode = requestCode;
    }

    public Resource getResource() {
        return this.resource;
    }

    public void setResource(Resource resource) {
        this.resource = resource;
    }

}

It seems that the GSON Converter cannot convert the class "Resource" that is self-defined by the server-side. I Google for a long time, some people point out that using deserializer. However, I still have no clues how to start with.

For more information: "Resource" is a class in the .jar file that be imported to android studio.

Anyone can give me some advice?