AppCenter.checkForUpdateAsync() method always returns null - flutter

Question

In my mobile app I use the AppCenter.checkForUpdateAsync() (flutter_appcenter_bundle package) method to check for updates and prompt the user to update the application if needed. However, the method always returns null, even if the current version is not the latest.
I tried to change the versions of the package, and in accordance with the documentation, I published applications with forced updates enabled. But it didn't help.
I have no more ideas what can be done.
The method checkForUpdateAsync is called when the button is clicked.
Details:
Future<void> checkAppUpdate() async {
final result = await AppCenter.checkForUpdateAsync(); // always returns null
logger.i(LogMessage('result $result', name: 'checkAppUpdate'));
if (result == null) {
showDialog(
context: context,
builder: (BuildContext context) => AlertDialog(
content: Column(
mainAxisSize: MainAxisSize.min,
children : <Widget>[
Container(
child: Text(
"Текущая версия приложения актуальна",
textAlign: TextAlign.center,
style: TextStyle(height: 1.44)
),
),
SizedBox(height: 20),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
RaisedButton(
child: Text('Ок'),
onPressed: () => Navigator.of(context).pop()),
])
],
),
)
);
}
}
Flutter version 1.12.13+hotfix.6
flutter_appcenter_bundle: 3.1.1+1