Hello @pajay,
Basically, when you create a KS [Kaltura Session], you need to pass the expiry param. If you set it to null, the default is 86400 [one day].
When the KS is no longer valid, you will get an exception.
For more info about creating sessions, see https://developer.kaltura.com/workflows/Generate_API_Sessions/Authentication
You may also be interested in the appToken mechanism, which you can learn about here:
https://developer.kaltura.com/workflows/Generate_API_Sessions/App_Token_Authentication