How should an educational application handle payment confirmation before granting access?

What is the recommended approach to confirming a Paynova payment before granting access to a paid feature in an educational application?

The use case is an online academic writing assistant with paid access to structured draft feedback. I would like to understand how payment status should be handled when a customer completes checkout but closes the browser before returning to the application.

Should the backend rely on a server-side notification, retrieve the payment status through the API, or combine these approaches? Which payment status should be treated as sufficient to activate access?

I would also appreciate guidance on handling duplicate notifications and delayed status updates so that the application does not activate access twice or leave a completed payment unrecognized.

Is there a documentation section or integration example covering this workflow?