Keynote background music across multiple specific slides

Hey guys. I am a complete noob. I need to make a complex presentation on keynote that needs some background music across specific slides. There is currently not an option to do this inside keynote. Searching online I found this
The idea is perfect but I can´t get it to work. It asks me for the playlist, it activates keynote but when starting the presentation (which has the correct song title on the presenter notes) nothing happens. Perhaps something to do with the version (I´m using latest on both keynote and itunes). Please help me.

What is contained by your playlist ?

At my first try, I selected a playlist containing Apple Music tunes and the machine stay silent.
So, I played a bit with different features until I got a warning saying that Keynote is not allowed to play Apple Music tunes which are protected.

Given that, I made other attempts with playlists containing tunes grabbed from youtube or bought from Amazon and it worked.

Yvan KOENIG running High Sierra 10.13.6 in French (VALLAURIS, France) mardi 25 février 2020 17:52:18

Oops, I was too optimistic. Now I am unable to switch from the playlist with youtube tracks to an other one when I ask Keynote to play the presentation.