Unity Rewarded Ads not showing up?

Everything is set up and the ads are working but i just placed my game in the play store and it showed the ad once and when i tried once again from different device it does not work.

Same with me. I just can play the ads 3 times and then, stop working.
This is happen when i use iOS devices. When I use, with the same code in my android device it works propperly.
What is happening?