How do I store / check a valid user session?

If you create a user session, the session will expire in 2 hours after the last request to the QuickBlox API. After this you will receive a "Required session does not exist" message. In this case the session should be recreated manually (i.e. you will need to submit a new request in order to create a session).

To create a session please review the corresponding section in our official documentation:
Server API - Authentication
iOS SDK - Authentication | iOS SDK | QuickBlox
Android SDK - Authentication | Android SDK | QuickBlox
JavaScript SDK - Authentication | JavaScript SDK | QuickBlox
React Native SDK - Authentication | React Native SDK | QuickBlox
Flutter SDK - Authentication | Flutter SDK | QuickBlox

To check the session expiration date see the following sections:
Server API - Authentication

Android SDK - Authentication | Android SDK | QuickBlox
JavaScript SDK - Authentication | JavaScript SDK | QuickBlox
React Native SDK - Authentication | React Native SDK | QuickBlox
Flutter SDK - Authentication | 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.