When trying to handle Client side routing for your React App hosted on IIS say using react-router-dom, you might need to handle situations where users access specific sections of your App like http://testapp/courses. Users might even save these URLs in their favorites and try to access them later.

This problem is not known while debugging the App in localhost until you host the App on an IIS Server. Since your React App is a Single Page Application (SPA), the Server is unaware of any static files like courses and will give 404 error. To solve this, send all your requests back to IIS with URL rewrite to the index.html static file and let the React App handle the routing.

First install the URL Rewrite module on the IIS Server. Then create a web.config file for your App or create a new one with code as shown below:

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
    <system.webServer>
		<rewrite>
		  <rules>
			<rule name="ReactRouter Routes" stopProcessing="true">
			  <match url=".*" />
			  <conditions logicalGrouping="MatchAll">
				<add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />
			  </conditions>
			  <action type="Rewrite" url="index.html" />
			</rule>

		  </rules>
		</rewrite>
    </system.webServer>
</configuration>

This should work well for your App when the user tries to access a Client side route and refresh the page or when trying to access the route later.