A shortened youtu.be address can identify the same video as a longer watch URL. You do not need to expand it manually when its video identifier is intact.
Copy the actual address
Use the video's share action and copy the link. Paste it into ToolNivo without quotation marks or extra commentary. A shortened link normally places the identifier immediately after the domain; an incomplete address cannot be repaired by guessing the missing characters.
Check the result
Request the thumbnail and compare the preview with the video you intended to inspect. Sharing links may contain additional parameters, but those do not represent a different image resolution. Choose the resolution from the tool's results instead.
Keep a useful record
When saving for your own archive, store the original video URL beside the downloaded image. A filename alone may not preserve enough context to identify it later. If the preview is wrong, return to the source video and copy its link again before troubleshooting the image itself.