iOS App Performance Fix

I'm looking for an experienced iOS developer to resolve performance issues in our mobile application, specifically related to payment gateway errors and the submission to the app store.

Key Requirements:
- Fix payment gateway errors affecting transactions.
- Ensure smooth and error-free payment processing.
- Improve app performance and reliability.

Ideal Skills and Experience:
- Proficiency in iOS development (Swift, Objective-C).
- Strong understanding of payment gateways and integration.
- Experience in debugging and optimizing app performance.
- Knowledge of backend services and API interactions.

Please provide examples of similar work done and your approach to solving these issues.