If anyone here facing same issue, isRewardedVideoAvailable always being false. I was initializing like this: LevelPlay.Init("appKey"); Changing initialization to this solved my problem:

LevelPlayAdFormat[] legacyAdFormats = new[] { LevelPlayAdFormat.REWARDED, LevelPlayAdFormat.INTERSTITIAL, LevelPlayAdFormat.BANNER };
LevelPlay.Init("appKey", adFormats: legacyAdFormats);