I think my game is little hard so i want my users to continue where they failed by watching video for only one time or continue using rare keys which is collectible for only one time
Ok, and your question is? You want to know how to do it. Or are you just telling us what your going to do? Anyway, either either, you can search the forum as it has been discussed many times, and you will find your answer, on how to set it up.
I am asking and What if i have set and next checkpoints in the scene and i want my user to continue where they died I cant find this anywhere
https://www.buildbox.com/forum/index.php?threads/watch-video-ads-on-gameover-screen.2202/#post-13881 two second search