Android Rewarded ads not loading

[imineti]

EDIT: I have updated this post as I have narrowed down the problem.

I have this function to load the rewarded video.

GoogleMobileAds_LoadRewardedVideo("ca-app-pub-9207854532541194/7731898672");

For some reason after I call this function the ad doesn't load.

I have this in the asynchronous social event to show a message if it has loaded or if there is an error.

var _id = async_load[? "id"];
   if _id == GoogleMobileAds_ASyncEvent{
   var ident = async_load[? "type"];
   switch (ident){
 
        case "rewardedvideo_adloaded":
               rewarded_loaded = 1;
               show_message_async("Rewarded ad loaded!"); // DEBUG
        break;

       case "rewardedvideo_loadfailed":
           show_message_async("Error Code: " + string(async_load[? "errorcode"]));
           //GoogleMobileAds_LoadRewardedVideo(ad_startWeek_id);
        break;

  }

When I try to load the ad I get the message "Error Code: 3", does anybody know how to fix it?