API Integration Test Cases for payment solution

I need test cases for integrating with PSP API for checkout solution. The main purpose of these APIs is payments and data retrieval, specifically focusing on three key data points: user information, transaction details, and product data.

There is also features like shipping, etc. Plus order management.

Key requirements:
- Generate detailed test cases covering various scenarios mainly based on information from developer documentation pages and swagger.

Ideal skills and experience:
- Strong experience with REST APIs
- Experience with PSPs
- Proficiency in writing test cases
- Familiarity with data validation and integrity checks
- Experience with testing tools and frameworks

Please provide samples of previous work and relevant experience.