Advertisement.IsReady not working

Yes I am working on the game for Android platform.
Yes I am using UnityEngine.Advertisements;
Yes I initialized Advertisement.Initialize(gameID);
and Yes my Ads package is up to date (4.0.0)
Also it is turned on
Mostly everything that is needed for the Advertising function is set up but for me to able to make the ad fully watched for rewards, I need to use the Advertisement.IsReady function but the Advertisement function can’t seem to find any function for it. It just says Advertisement does not contain a definition for IsReady. Did Unity remove this function or did I just forget something important?

OK I figured it out thanks to FC12C!!! For anyone whos having the same problem as I have DO NOT GET THE 4.0.0 LATEST VERSION AD MANAGER. The functions happen to work on every package versions except the latest one. Hope you guys have a great hoilday!

I Just Had This Problem Too, Luckily It Was A Easy Fix (for me anyway) i just went to package manager and updated it to 3.5 or newer,I Just Had This Problem Too, Although Mine Was On 4.0.0 Update It To 3.5 or newer. this worked for me