Form url encoded

Use @Field annotation to provide key-value pairs

    @FormUrlEncoded
    @POST("/users/repos")
    void fetchRepoBySearch(
          @Field("page") int pageNumber,
          @Field("sort") String sort,
          Callback<Repo> callback
    );

    service.fetchRepoBySearch(2,"asc", callback);
    //output url is ENDPOINT/users/repos?page=2&sort=asc

@FieldMap is used to add fields by map

    @FormUrlEncoded
    @POST("/users/repos")
    void fetchRepoBySearch(
          @FieldMap Map queryParamsMap,
          Callback<Repo> callback
    );

    Map<String,String> map = new HashMap<>();
    map.put("sort","asc");
    map.put("offset", "100");

    service.fetchRepoBySearch(map, callback);