Worked on the laravel/cashier-stripe repository to enhance stability and backward compatibility for merchants using legacy Stripe payment methods. Addressed a critical bug by implementing Stripe Source compatibility within the fillSourceDetails function, which prevented TypeErrors when handling older payment sources. This backend development effort, using PHP and Stripe integration skills, ensured that legacy Source payment methods could be managed alongside newer Card and BankAccount types during Stripe API migrations. The update improved reliability for merchants updating their default payment methods and contributed to maintainability by providing clearer commit documentation and traceability for backward-compatibility changes throughout the codebase.