I started a collaborative playlist so my husband and I could both put songs on it. Neither one of us can figure out how he can add a song to this playlist!

He has a Chromebook so can only use the web version of Spotify and the navigation is not as good as (and different from) what I see using the app for Mac.

I've sent him the playlist link and he can pull it up and play it. But when he wants to add a song and clicks on the elipses, it gives the "add to playlist" option, but then there's no option to add to that playlist, only to create a NEW playlist. You can't search for an existing, collaborative one.  There's no option to add a song while looking at the playlist page itself. 

We are on the Spotify premium family plan. I've checked to make sure that the playlist is collaborative. 

Ugh. Please advise.