Revamp C# MVC Web App Custom APIs

I have C# MVC Web App that works using SQL Server Database & using APIs at the same time.

For the functions that use the database, I want to replace them with the APIs

1- Error message appear with no details, need to make the error message has Show More to display the details of the error.

2- Load Codes from APIs instead of loading from JSON file. (1 API) require updating treeview to load on demand

3- Packages Load from APIs instead of loading from DB (2 APIs)

4- SubscribedPackages Call API instead of inserting into a DB (1 API)

5- Schemes Load from APIs instead of loading from DB (1 API)

6- Uploads Call API instead of inserting into a DB (1 API)

7- Users Call API instead of inserting and reading from a DB (5 APIs)

you must have C# MVC experience.

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I urgently need expertise in fixing my C# MVC web application that's currently working with custom APIs. Unfortunately, there is an ongoing issue that needs immediate resolution.

Key Requirements:
- A deep understanding of C# MVC; proficiency in managing custom APIs
- Ability to diagnose and remediate a range of application errors swiftly
- The capacity to deliver high-quality work on a tight schedule

Project completion is a high priority; therefore, I am seeking a swift solution. Your prompt response will be highly appreciated.