Cannot make java object from python using pyjnius

Question

I'm trying to get rewarded ads to work on kivy using pyjnius by following the example by google (https://github.com/googleads/googleads-mobile-android-examples/tree/main/java/admob/RewardedVideoExample) to create a loadRewardedAd function and a showRewardedVideo function.

from jnius import autoclass, PythonJavaClass, java_method
from kivy.logger import Logger

RewardedAdLoadCallback = autoclass("com.google.android.gms.ads.rewarded.RewardedAdLoadCallback")

class RewardedVideoAdListener(RewardedAdLoadCallback):

    __javacontext__ = 'app'
    __javaclass__ = "com/google/android/gms/ads/rewarded/RewardedAdLoadCallback"

    __INFO = True

    @java_method('(Lcom/google/android/gms/ads/AdError;)V')
    def onAdFailedToLoad(self, loadAdError):
        if self.__INFO:
            Logger.info("AdMob: onAdFailedToLoad")

    @java_method('(Lcom/google/android/gms/ads/rewarded/RewardedAd;)V')
    def onAdLoaded(self, rewardedAd):
        if self.__INFO:
            Logger.info("AdMob: onAdLoaded")


class Ads:
    def __init__(self, AD_UNIT_ID="ca-app-pub-3940256099942544/5224354917"):
        self.rewarded_ad = None
        self.is_loading = False
        self.AD_UNIT_ID = AD_UNIT_ID

    def load_rewarded_ad(self):
        if self.rewarded_ad is None:
            self.is_loading = True

            RewardedAd = autoclass("com.google.android.gms.ads.rewarded.RewardedAd")
            AdRequestBuilder = autoclass('com.google.android.gms.ads.AdRequest$Builder')
            activity = autoclass('org.kivy.android.PythonActivity')

            ad_request = AdRequestBuilder().build()

            RewardedAd.load(
                activity,
                self.AD_UNIT_ID,
                ad_request,
                RewardedVideoAdListener()
            )

Among other things such as a huge coredump I get this error which I think is the most relevant.

04-14 02:22:52.732 16008 25520 F org.test.myapp: runtime.cc:677] JNI DETECTED ERROR IN APPLICATION: can't make objects of type com.google.android.gms.ads.rewarded.RewardedAdLoadCallback: 0x12caeb18
04-14 02:22:52.732 16008 25520 F org.test.myapp: runtime.cc:677]     in call to NewObjectA
04-14 02:22:52.732 16008 25520 F org.test.myapp: runtime.cc:677]     from int org.libsdl.app.SDLActivity.nativeRunMain(java.lang.String, java.lang.String, java.lang.Object)

What is the reason I cant make objects of type RewardedAdLoadCallback?