If you are using volley for android as described in this post, you may have to set headers to get the wanted response from your server.

Therefore you just have to add after the wanted request an Map, that returns the desired headers:

JsonObjectRequest jsonObjectRequest = new JsonObjectRequest( ... ) {
    @Override
    public Map<String, String> getHeaders() {
        Map<String, String> params = new HashMap<String, String>();
        params.put("x-vacationtoken", "secret_token");
        params.put("content-type", "application/json");
        return params;
    }
};

Code Example

String url = "http://httpbin.org/post";

//create post data as JSONObject - if your are using JSONArrayRequest use obviously an JSONArray :)
JSONObject jsonBody = new JSONObject("{\"message\": \"Hello\"}");
 
//request a json object response
JsonObjectRequest jsonRequest = new JsonObjectRequest(Request.Method.POST, url, jsonBody, new Response.Listener<JSONObject>() {
    @Override
    public void onResponse(JSONObject response) {
 
        //now handle the response
        Toast.makeText(MainActivity.this, response, Toast.LENGTH_SHORT).show();
 
    }
}, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
         
        //handle the error
        Toast.makeText(MainActivity.this, "An error occurred", Toast.LENGTH_SHORT).show();
        error.printStackTrace();
 
    }
}) {    //this is the part, that adds the header to the request
    @Override
    public Map<String, String> getHeaders() {
        Map<String, String> params = new HashMap<String, String>();
        params.put("x-vacationtoken", "secret_token");
        params.put("content-type", "application/json");
        return params;
    }
};
 
// Add the request to the queue
Volley.newRequestQueue(this).add(jsonRequest);