Error uploading with FireBaseStorage.net with Xamarin

I developed the following routine to upload images.

         var task = new FirebaseStorage("xxxxxx.appspot.com")
             .Child("data")
             .Child("random")
             .Child("file.png")
             .PutAsync(img);

When I try to send I receive the following message:

Exception occured while processing the request.
Url: https://firebasestorage.googleapis.com/v0/b/xxxxxxx.appspot.com/o?name=data%2Frandom%2Ffile.png
Response: N/A