Polyline between to locations not snapped to road

I’m trying to draw a smooth polyline between two locations that are some distance apart (say over 100 miles) on a Google Map in Android. I’ve been following this guide and also this guide in terms of utilising the Directions and Snap to Roads API, yet due to the limit of 100 coordinates from the Snap to Roads API, it appears it is virtually impossible to draw a smooth polyline from one location to another that follows the smooth contours of the road.

I’ve managed to extract all coordinates of the directions to plot a polyline using the returned overview_points and have decoded this using the decode method from the PolyUtil API, yet the polyline drawn on the map is not snapped to the road for the vast majority of the time. Instead, I’ve tried using the Snap to Roads API and set a limit of 100 coordinates (maximum GPS points allowed) that all seem to be very accurately snapped to the road from destination A to B (only covering some distance between the two locations if far apart).

Basically, is there something I am missing entirely, or is it a case of coming up with some resolution to spread the 100 coordinates allocation of the Snap to Roads API using the GPS points retrieved from the overview_points from the Directions API, i.e. plot a coordinate every XXX meters.

Here is the bulk of the code I’ve implemented through a Volley request minus the Snap to Roads request, which the later is fairly straightforward to implement:

StringRequest stringRequest = new StringRequest(Request.Method.GET, 
            new Response.Listener<String>() {
                public void onResponse(String response) {

                    JSONObject directions;
                    try {
                        directions = new JSONObject(response);

                        JSONArray routes = directions.getJSONArray("routes");

                        mCoordinates = new ArrayList<>();
                        for (int i = 0; i < routes.length(); i++) {
                            JSONObject routesObject = routes.getJSONObject(i);

                            JSONObject overviewPolyline = routesObject.getJSONObject("overview_polyline");
                            String points = overviewPolyline.getString("points");
                            String formattedResponse = points.replaceAll("'\'", "''");

                            List<LatLng> coordinates = new ArrayList<>();

                            PolylineOptions routeCoordinates = new PolylineOptions();
                            for (LatLng latLng : coordinates) {
                                routeCoordinates.add(new LatLng(latLng.latitude, latLng.longitude));

                            Polyline route = mGoogleMap.addPolyline(routeCoordinates);
                            for (LatLng latLng : coordinates) {
                                mGoogleMap.addMarker(new MarkerOptions().position(new LatLng(latLng.latitude, latLng.longitude)));


                    } catch (JSONException e) {

            }, new Response.ErrorListener() {
        public void onErrorResponse(VolleyError error) {
            // TODO handle error