My current web application needs a round of polish and two new integrations. First, the core adjustments: • User interface updates – refine layouts, improve visual consistency, and make the flow more intuitive on both desktop and mobile. • Performance optimization – cut load times, streamline API calls, and make sure assets are compressed and cached properly. • Bug fixes – eliminate the lingering front-end and back-end errors that occasionally throw 4xx/5xx responses or break UI components. Second, the integrations: • Payment gateway – wire in a mainstream provider such as PayPal, Stripe, or Square. The codebase is already modular, so you can slot in the SDK or REST API that best matches our tech stack and regional availability, then run test transactions in the sandbox before going live. • Invoicing – hook the app to a cloud accounting service (QuickBooks, Xero, or FreshBooks). I’ll provide API credentials; your task is to sync customer data, push paid invoices automatically, and confirm that invoice PDFs are generated and stored.