Odnoklassniki app for a group. No response to OKSDK.Widgets.askGroupAppPermissions('MESSAGES_FROM_GROUP'). Why?

Question

Classmates

No response to OKSDK.Widgets.askGroupAppPermissions('MESSAGES_FROM_GROUP') without passing return_url
Tried both via API_callback and via:
window.addEventListener('message', function (widgetMessage) {
console.log(widgetMessage);
// process the message from the widget here
}, false);
In both cases, there are no notifications.