You've been given this codebase for a courier service application. Imagine you're joining a team that's maintaining this application and they've asked for your input to improve the code. The service is already running in production in Amazon ECS. Please review the project, and based on what you see:

1. Identify as many design or implementation flaws in the code as you can.
2. Explain why they are problematic.
3. Demonstrate how you would fix one of these flaws. Implement the changes directly in the code and explain your reasoning as you go.