NullReferenceException: Object reference not set to an instance of an object

Hello everyone, I hope your help. I have this type of problem and I don’t know how to solve it

NullReferenceException: Object reference not set to an instance of an object
AdsController.OnAdmobRewarded (System.Object sender, GoogleMobileAds.Api.Reward args) (at Assets/PictureQuizPlus/Scripts/Monetization/AdsController.cs:782)

There are several things missing from your question but I think I have figured some of them out. NullReferenceException is a runtime error and would strongly imply that rewardedCallback has not been initialised.

Line 782 appears to be a call to a method, since you have written rewardedCallback(...). However, line 787 would imply that rewardedCallback is a variable that you are setting to null. Is that correct?

These are incompatible with each other and I would have expected your IDE to raise an error. It would help if you could clarify what rewardedCallback is and have a look at these statements.

The initialisation of the struct looks correct and using it as a parameter to a method is fine so no problems there.