Why is App Check Admin SDK rejecting debug tokens?

Question

I am using App Check with my Flutter Android debug App to validate my app with my Cloud Run Node API. I followed the steps required to get and add the debug token to the Firebase Console Admin UI but it is rejecting my requests. Here is my backend code:

const authenticate = async (req, res, next) => {
    const appCheckToken = req.header('X-Firebase-AppCheck');
    if (!appCheckToken) {
        res.status(401);
        return next('Unauthorized');
    }
    try {
        const appCheckClaims = await firebaseAdmin.appCheck().verifyToken(appCheckToken);

        // If verifyToken() succeeds, continue with the next middleware
        // function in the stack.
        return next();
    } catch (err) {
        res.status(401);
        return next('Unauthorized');
    }
}

And my main method in Flutter:

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp(
    options: DefaultFirebaseOptions.currentPlatform,
  );
  await FirebaseAppCheck.instance.activate(
    webRecaptchaSiteKey: 'recaptcha-v3-site-key',
    // Default provider for Android is the Play Integrity provider. You can use the "AndroidProvider" enum to choose
    // your preferred provider. Choose from:
    // 1. debug provider
    // 2. safety net provider
    // 3. play integrity provider
    androidProvider: AndroidProvider.debug,
  );
  runApp(const MyApp());
}