Worked on stabilizing subscription data integrity in the laravel/cashier-stripe repository by addressing a bug affecting quantity propagation for Single Price subscriptions. Focused on backend development using Laravel and PHP, the work involved fixing how quantity updates to a subscription item are synchronized between the subscription and subscription_items tables, eliminating data inconsistencies and potential billing errors. Developed targeted test coverage to reproduce the issue and verify the solution, ensuring ongoing regression protection. Updated the code path for the 16.x branch to improve quantity handling, resulting in enhanced billing accuracy and more reliable reporting for subscription management workflows within the system.