无法转换java.lang.String类型的值

Am retrieving data from MySQL table using Android HttpURLConnection And am getting this error:

W/System.err: org.json.JSONException: Value br of type java.lang.String cannot be converted to JSONObject

Error is at this line:

JSONObject jsonObj = new JSONObject(myJSON);

my code:

 try {  

        JSONObject jsonObj = new JSONObject(myJSON);

        Challenges = jsonObj.getJSONArray(TAG_RESULTS);

        for (int i = 0; i < Challenges.length(); i++) {


            JSONObject c = Challenges.getJSONObject(i);

            String id = c.getString(TAG_ID);
            String trackCoordinates = c.getString(TAG_COORDINATES);

            HashMap<String, String> challengesFromDB = new HashMap<>();

            challengesFromDB.put(TAG_ID, id);
            challengesFromDB.put(TAG_COORDINATES, trackCoordinates);

            ChallengesList.add(challengesFromDB);
        }

.php file:

    $sql = "select * FROM Challenges";

$res=mysqli_query($con, $sql);

$result=$array();

while($row = mysqli_fetch_array($res)){
array_push($result,array('id'=>$row[0],'userMail'=>$row[1],'trackCoordinates'=>$row[2]));

}

header('Content-Type: application/json');
print json_encode(array("result"=>$result));

mysqli_close($con);

Maybe error occuring because of my table field:trackCoordinates , am storing here googleMaps latitude, longtitude coordinates array, for example:

[lat/lng: (54.892597770959945,23.87877881526947), lat/lng: (54.89242519582151,23.876227363944054), lat/lng: (54.8917038430203,23.877791762351986)] 

You aren't getting JSON, you're getting html. Either something on your server is outputting html, or you're hitting the wrong URL.