Just to be clear: you never had any ads or they stopped working in some point? Do you know where to watch?

Watching those video ads give you free rest packs, morale boosters, treatment packs and even money. They can be watched from the same location where you can buy those same things with tokens. So when you open 'Rests' page, there should be 'Get free' button in the bottom left corner. If it's black, then there's no videos to watch, if it's blue just push it to watch the video ad and you will be granted one rest pack. Same thing with morale boosters etc.

You can also watch video ads all the same places you can restore your players condition with rest packs, like the players personal page.