Webapp Enhancement and Payment Integration

I need a skilled developer to complete and enhance my existing webapp. The primary focus is on fixing broken code, but also includes user testing, making it phone-friendly, updating features, and integrating Stripe for payments.

Key Tasks:
- Code Review and Fixes: Identify broken areas and apply necessary fixes.
- User Testing: Conduct testing with real users to ensure functionality.
- Adaptability Changes: Optimize for various devices, especially phones.
- Feature Update: Modify and enhance existing features as required.
- Payment Integration: Incorporate Stripe.

Ideal Skills and Experience:
- Proficiency in web development and debugging.
- Experience with user testing and feedback implementation.
- Knowledge of mobile optimization.
- Familiarity with Stripe and payment gateway integration.
- Strong problem-solving skills.

Please provide a portfolio showcasing similar projects. Looking forward to your bids!