Android : why gettting java.io.FileNotFoundException Error

I use HttoUrlConnecton in my anroid project to fetch json data from web service

I test this app for 1 week but today I get the FileNotFoundException error when I want to fetch data from myUrl and this my log

 java.io.FileNotFoundException: myUrl
        at com.android.okhttp.internal.http.HttpURLConnectionImpl.getInputStream(HttpURLConnectionImpl.java:186)
        at com.example.mehrdad.FetchData.doInBackground(FetchData.java:232)
        at com.example.mehrdad.FetchData.doInBackground(FetchData.java:41)
        at android.os.AsyncTask$2.call(AsyncTask.java:288)
        at java.util.concurrent.FutureTask.run(FutureTask.java:237)
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
        at java.lang.Thread.run(Thread.java:841)

I get getResponseMessage and getResponseCode and I get response code 403

and I get Forbidden message

but When I use browser everything is right!!

I iterate my project over and over and over !! but any progress! and I tried!

any idea?!