Fix Flutter Membership Bug

My Flutter-based fitness app connects to a Laravel 9 backend and handles in-app memberships. At the moment, the flow breaks right after a user pays: the purchase goes through, but the app immediately asks them to buy again as if the subscription were never created. I have already reproduced the issue in a staging environment and confirmed that the problem happens every time—straight after purchase, before the user even restarts the app.

What I need from you is a clean, well-documented fix that:

• correctly stores and verifies the subscription on the Laravel side
• updates the Flutter client so it recognises the active membership without prompting again
• is delivered via Git pull request (backend and mobile), with brief notes outlining the changes and any migration steps

I will provide full repository access, test credentials for the sandbox, and examples of successful payment payloads. Once your patch is deployed to staging, I’ll verify that a single purchase unlocks the paid features and survives normal app use without duplicate prompts.