Browsing WEB API in IIS

Normally, this kind of web-related-it-works-in-dev-but-fails-in-prod problem is down to one of two things:
1) User / permissions. In dev, you C# code runs as you on your machine, and can access anywhere you can. In prod, it runs under a specific user for IIS, and it's permissions are very restricted - pretty much only the folder that your code is located in and it's subfolders are accessible at all!

2) Assuming that C# and JS code run on the same machine: they don't. C# code runs on the server and can only access files and devices connected directly to that machine and it's local LAN. JS code runs on the client and can only access a limited part of that machine via the browser.
In dev, that works OK because both machines are the same physical computer. In prdo the two computers could be thousands of mines apart!
For example, a MessageBox in C# code looks fine in dev, but in prod it is shown on the Server where the client can see it, and can't respond to it even if he guesses it should be there.

We don't have any access to your code, so we can't tell you how to fix it: you will have to fall back on an old form of debugging: add logging code to show you what is actually happening in production, and review the logs after the problem has occurred. Refine your logs to "narrow down" the problem, and repeat until you can work out what is happening when it shouldn't, or not happening when it should.

Sorry, but we can't do any of that for you!