Copying and pasting the full URL will not work here. You will instead need the Share URL.
Accessing the Share URL
1. Find your desired video on YouTube.
2. Click on Share found under the right corner of the video
A pop-up will be generated containing the video's shareable URL.
Want only the chorus or a section of the video?
3. Update the Start At time if desired, and click Copy.
4. Paste the URL into the Anthem URL field (this is found within My Settings). Click the blue Test button to preview your anthem within Ambition.
5. Once satisfied with your Anthem, click the green Save Changes button at the bottom of your settings.