应用广告加载失败求助：start.io等平台返回onFailedToReceiveAd

我的应用无论在测试模式还是从谷歌Play商店下载后，均无法显示广告。尝试了start.io、Unity等多个广告平台，要么出现空白加载界面，要么像start.io平台始终返回onFailedToReceiveAd错误。

三周前start.io广告还能正常展示，我多次修改代码、重新集成SDK、配置权限并更新gradle.build，但问题仍未解决。已联系start.io官方4天，对方表示正在处理，但暂无进展，恳请提供技术帮助。

以下是此前可正常运行但现在失效的start.io激励视频广告代码（仍返回onFailedToReceiveAd(Ad ad)错误）：

import android.os.Bundle;
import android.widget.Toast;

import com.startapp.sdk.adsbase.Ad;
import com.startapp.sdk.adsbase.StartAppAd;
import com.startapp.sdk.adsbase.StartAppSDK;
import com.startapp.sdk.adsbase.VideoListener;
import com.startapp.sdk.adsbase.adlisteners.AdEventListener;

import androidx.appcompat.app.AppCompatActivity;

/*13/12/22*/

public class Pub1b extends AppCompatActivity {

    private StartAppSDK startAppAd = new StartAppSDK();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        StartAppSDK.init(this, "xxxx_ap_id", false);
        StartAppSDK.setTestAdsEnabled(true);
        StartAppSDK.setUserConsent (this,
                            "pas",
                            System.currentTimeMillis(),                        
                            true);
    StartAppSDK.setUserConsent (this,  
                            "pas",
                            System.currentTimeMillis(),                        
                            false);
        final StartAppAd rewardedVideo = new StartAppAd(this);
        rewardedVideo.setVideoListener((VideoListener) () -> {
            Intent intent = new Intent(Pub1b.this, Ind1b.class);
            startActivity(intent); 
            finish();
        });
        rewardedVideo.loadAd(StartAppAd.AdMode.REWARDED_VIDEO, new AdEventListener() {

             @Override
            public void onReceiveAd(Ad arg0) {
                rewardedVideo.showAd();
            }
            @Override
            public void onFailedToReceiveAd(Ad ad) {
                Toast.makeText(Ub1b.this, getString(R.string.zjj), Toast.LENGTH_LONG).show();
                Intent intent = new Intent(Pub1b.this, Helpp1b.class);
                startActivity(intent); 
                finish();
            }
        });
    }
}

内容的提问来源于stack exchange，提问作者Anna-laura