public interface UserService {
    @POST(Constants.Api.URL_REGISTRATION)
    @FormUrlEncoded
    BaseWrapper registerUser(@Field("first_name") String firstname, @Field("last_name") String lastname, @Field("regNumber") String phone, @Field("regRole") int role);


 public BaseWrapper registerUser(User user) {
        return getUserService().registerUser(user.getFirstName(), user.getLastName(), user.getPhone(), user.getRole());
    }

此创建异常

 com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $

非常感谢您的帮助。