Music tracks with a Content ID tag are not licensed for use in monetized YouTube videos. If you want to use such a track, please contact Icons8 support, and we will ask permission from the rights holder. When the permission is granted, you will be able to use this track in a monetized YouTube video.
To avoid delays, we recommend using tracks without a Content ID tag, as these can be used on YouTube without additional permissions.
You can find more information about Content ID in this article.
Also, you can check out this article about using our music in paid online ads.