Add support for directions responses with "geojson" geometries

I am working on a project where our users will be sharing the same route and use Mapbox in their client apps for navigation.
Since it is important for us to use the same route, it was decided to generate route on a backend side and clients were suppose to download route in json format, parse it and give route to Mapbox Navigation SDK.
I tried to solve this task in 2 ways.

1. Using REST API

I tried to use your REST API for generating a route and it works well, but when I try to parse JSON using DirectionsRoute.fromJson(String json) method I am getting an exception

Expected a string but was BEGIN_OBJECT at line 1 column 969 path $.legs[0].steps[0].geometry

although JSON itself has a valid format.

2. Using Java SDK

On a backed side I was generating a route, but using Mapbox SDK:

String accessToken =
                "accees_token";

        Point originPoint = Point.fromLngLat(**, **);
        Point destinationPoint = Point.fromLngLat(**, **);

        MapboxDirections client = MapboxDirections.builder()
                .origin(originPoint)
                .destination(destinationPoint)
                .overview(DirectionsCriteria.OVERVIEW_FULL)
                .profile(DirectionsCriteria.PROFILE_WALKING)
                .accessToken(accessToken)
                .build();

client.enqueueCall(new Callback<>() {
            @Override
            public void onResponse(Call<DirectionsResponse> call, Response<DirectionsResponse> response) {

                DirectionsRoute directionsRoute = response.body().routes().get(0);
                Gson gson = new Gson();
                String json = gson.toJson(directionsRoute, DirectionsRoute.class);

            }

            @Override
            public void onFailure(Call<DirectionsResponse> call, Throwable throwable) {
                System.out.println("Error: " + throwable.getMessage());
            }
        });

But this time converting DirectionsRoute to json returns {}, although route array is not empty.

I only need to generate route on backend side as json and use that route on client side.
Any of these solutions are suitable for us if they will work properly.
Could you help me resolve any of them?

Beginne mit dem Einstiegspunkt DirectionsRoute.fromJson(String json) und dem im Bericht beschriebenen MapboxDirections-Antwortmodell. Verfolge, wie die Geometrie eines Wegpunkts einer Wegbeschreibung geparst wird und wie eine DirectionsRoute serialisiert wird; abgeschlossen ist die Arbeit, wenn Routen mit GeoJSON-Geometrie für die Verwendung durch Clients geparst und serialisiert werden können, ohne dass die gemeldete Ausnahme oder leeres JSON auftritt.