One Drive API returns invalid Access Token - onedrive

Question

The authentication process is not working now.(It was working earlier). By following the documentation I'm trying to get the access token from a refresh token. I successfully can get a access token. But it's not valid. I'm setting it as Bearer and send it in my GET request and it returns the following JSON
{"error":{"code":"accessDenied","message":"Access Denied"}}
Here is the code sample
String messageBody = "client_id=" + "9b1a6dbb-7e1f-41b5-b448-9f328169411e" + "&redirect_uri=" + returnURL + "&client_secret={cleindsecret}
+ "&refresh_token={refreshtoken}&grant_type=refresh_token";
RequestBody oAuthCodeRedeemBody = RequestBody.create(MediaType.parse("application/x-www-form-urlencoded"),
messageBody);
Request request = new Request.Builder().url("https://login.live.com/oauth20_token.srf")
.post(oAuthCodeRedeemBody).build();
String responseBody = null;
OkHttpClient client = new OkHttpClient();
client.setFollowRedirects(false);
Response response;
String accessToken = null;
try {
response = client.newCall(request).execute();
responseBody = response.body().string();
resp = (JSONObject) jsonParser.parse(responseBody);
} catch (IOException | ParseException e) {
e.printStackTrace();
}
accessToken = (String) resp.get("access_token");
I'm getting a Access Token here. But I can't use it to do any work.
Request request2 = new Request.Builder().url("https://api.onedrive.com/v1.0/drive/items/1ED8983F38E94F01!107/children").header("Authorization", "Bearer " + accessToken).get().build();
The response for the above code is returned as
{"error":{"code":"accessDenied","message":"Access Denied"}}
What is the reason here. Is the API returning me a invalid access token or is something wrong in my code?