I recently created a playlist and made it collaborative on the desktop app. I then sent the playlist link to my friend who I intend to build the playlist with, they liked/followed it. When attempting to add songs however, the option was unavailable to them. None of the information that we've found online has helped in resolving this issue, so I'm hoping I can find some answers here.
It may be worth noting that my friend lives in the US- and while I know licensing can be different between our two countries, I would imagine that would be an issue on a song by song basis rather than something like this.