I need a seasoned developer to slot a fully-featured billing module into my live site without disrupting existing traffic or data. The current codebase is stable and well-documented; I’ll share the exact tech stack and repository access after we sign an NDA. Here’s what I expect from the engagement: • A seamless checkout flow that supports secure card processing, adjustable pricing logic, taxes, discounts, invoicing, and refund handling. • Clean integration with a mainstream gateway such as Stripe, Braintree, or PayPal (I’m open to your recommendation once you review the stack). • Dashboard screens where I can create and track plans, coupons, and transactions, plus a customer area for card updates and invoice downloads. • Webhook handling for events such as failed payments and subscription renewals, with email notifications wired into my existing SMTP service. • Clear, well-commented code that matches my current architecture, along with a short hand-off document and a walk-through call once you’re done. Testing and acceptance: The job is finished when automated tests pass and I can run through a full purchase, refund, and subscription renewal flow in staging, then flip the same build to production with zero errors in the logs. When you reply, focus on your experience integrating similar billing solutions—links to live sites, repositories, or screenshots are perfect. No need for long proposals; solid past work speaks louder.