URL Unauthorized access error while accessing files from dropbox?

I edited your post to remove the signature, but you may want to get a new app key and secret now that yours has been published here.

The signature that you originally posted looks broken... it should have an ampersand (&) at the end of it. (When URL-encoded, and ampersand ends up being a %26.) See https://blogs.dropbox.com/developers/2012/07/using-oauth-1-0-with-the-plaintext-signature-method/ for an example.

Hi I used PLAINTEXT but now it is not showing even single image thumbnail. but when i clicked on it it showing full image .

If I understand you correctly, you're no longer getting an "unauthorized access" error at all. Is that right?

If so, please explain the new issue you're seeing. Include the relevant code, what you expected to happen, and what actually happened.

No but now am getting Unauthorized Exception in case of showing thumbnails we are using this url( https://api-content.dropbox.com/1/thumbnails/auto ) It is always giving us above mentioned exception. How to get Thumbnails of Images from dropbox.

So you're still getting an "unauthorized error" message? Is this on all paths or still just the ones that include parentheses? Are you still using HMAC signing, or have you switched to PLAINTEXT?

Is it only /thumbnails that fails, or do other endpoints also fail?

Am using PLAINTEXT only. Yes it fails only for Thumbnails.

It is on all paths but only for Thumbnails.

Please share code for a call that works (something other than /thumbnails) and a call that doesn't work (/thumbnails).

For Thumbnails

string url = DriveUtilities.GenerateSignature(
    new Uri(string.Format(AppConstants.DropBox_GetThumbnail, item.serverFileId), UriKind.RelativeOrAbsolute),
            "GET", drive.AccessToken, drive.RefreshToken);
Stream fileStream = await FileHelper.getFileInputStream(url);

if (fileStream != null)
{
    try
    {
        if (fileStream.Length > 0)
            await FileSaveToStorage(fileStream, file);
        handler(fileStream);
    }
    catch (Exception ex)
    {
    }
}

for full image we are using this code (working)

WebProvider objWebProvider = new WebProvider();
string size = "?size=" + await CommonFunctions.GetThumbnailSize(DriveType.DROPBOX);
var uri = DriveUtilities.GenerateThumbviewSignature(
    new Uri(string.Format(AppConstants.DropBox_GetThumbnail, path) + size, UriKind.RelativeOrAbsolute),
            "GET", DropBox_AccessToken, DropBox_AccessTokenSecret);
url = uri.ToString();