There are multiple YouTube links to the same video. When a URL looks like this:

Shortened Version: https://youtu.be/U9izCJT5DGx
Original Version: https://www.youtube.com/watch?v=U9izCJT5DGx

You will need to use the Original Version of the URL. Just take the video ID (the numbers and letters after the / ) and add it after the ?v= in the original version.