The maximum number of subscriptions for one user is 10 and when a user exceeds this limit, it is not possible to create more subscriptions.
If you exceed the limit your application will receive the error 422 "Unable to create a subscription because of exceeded maximum subscriptions."
You can find more information how to create push notification subscriptions for each SDK here:
iOS SDK - Push Notifications | iOS SDK | QuickBlox
Android SDK - Push Notifications | Android SDK | QuickBlox
React Native SDK - Push Notifications (quickblox.com)
Flutter SDK - Push Notifications | Flutter SDK | QuickBlox
Feel free to check our official documentation for more information that will help you to integrate QuickBlox services into your applications / projects or contact our Support team by submitting a ticket if you have any other questions.