Alright, so I found out how to get it to work! (Only really know how to get Soundcloud urls working though, although this might work with youtube if it uses the same method)
1. get your soundcloud url example: https://soundcloud.com/artist/song
2. then get a soundcloud downloading site (I used): https://9soundclouddownloader.com/
3. paste your soundcloud in and all that until you get to a site where you can play your new mp3 file or download it.
4. Copy the insanely long link address and use an url shortener I used for example: goo .gl
5. Paste the long link address in and convert it to a short url
6. Go ingame and use the command/the contex menu to paste your new short link into boxvis.
And voila! It should now be working!