Creating a Custom API That Calls Another API Based on Response Code & .NET/C# Documentation

Hello everyone,
I'm currently working on a customization project in One Identity Manager and would like some guidance on the following:
I'm trying to create a custom API endpoint that will:
Call an external API.
Based on the response code (e.g., 200, 400, 500), decide whether to call a different API or return an appropriate result to the client.
Has anyone implemented something similar within the One Identity framework or via a custom web module?
Additionally, I'm looking for more detailed documentation or references related to .NET/C#, especially regarding the functions and classes used in One Identity's API development. The official documentation covers the basics, but I'm hoping to find something that explains the deeper capabilities and features (e.g., best practices for exception handling, async API patterns, extensibility points, etc.).
Any insights, examples, or links to resources would be greatly appreciated!
Thanks in advance!
Best regards.