So either this was just fixed or I might of found a way to fix it.
On pc play any video and change the settings from HTML5 to progressive playback, then close the video, now on ps4 it should work. Not sure if that is coincidence because it is working in HTML5 mode now on ps4 but it's worth a try if it's still broken for you.
Came here to report the same thing, I signed up to premo purely to watch content on my ps4 (2nd monitor is ps4 as my old ass PC only has 1 hdmi out).
Everything else works, you can even see a faint image of the video thumbnail in the background and the curser changes when hovering over the play button so it is acknowledging the video in some way, but nothing happens when clicking it.
My work around for anyone desperate enough has been to simply download on pc, transfer to usb and watch on ps4 from the usb.
I'm currently playing Orbusvr, which for those that don't know is an (the first ever?) mmorpg in vr.
If I'm honest the game is not fantastic, kinda fun but a bit wonky to say the least and the graphics are basic, cartoony and just a bit crap. However the community in the game is possibly the best community I have ever come accross. A quote I heard sums it up well: "The people in this game are nicer than anyone I've ever met in real life"
Even the kids are cool.
I'm only early into it and not sure if I'll stick with it but so far it's been such a pleasant and relaxing experience, a great clenser from the other game I'm playing, which is Saints and Sinners.