Can't watch remotely anymore

Hey guys, my questions is more about why was it working before rather than why isn't it working right now.

Ive never had plex premium or remote pass.

I have an account with two users created - main one and friend one. ​

Mt friend would login to same account, select that second user. I would invite second user to watch together and it worked. He is in completely different city. They were always using app.plex.tv website on their side.

They changed pc yesterday and since then they are getting error when trying to join saying they need plex premium.

Why was it working before?

Thanks for the help ​