Why is the rewarded callback not being called?

Question

I have this hook in my app. The ad is showing fine - both with test ads and with real ones. But the EARNED_REWARD listener is not firing. Anyone have any ideas why?

({ RewardedAd, RewardedAdEventType } = require('react-native-google-mobile-ads'));

 useEffect(() => {
      const unsubscribeLoaded = rewarded.addAdEventListener(RewardedAdEventType.LOADED, () => {
        setLoaded(true);
      });

      const unsubscribeEarned = rewarded.addAdEventListener(
        RewardedAdEventType.EARNED_REWARD,
        reward => {
          alert('User earned reward of ', reward);
          rewarded.load();
        },
      );
      rewarded.load();
    }, []);