Ensure that the URL you want to monitor is accessible from the machine where Applications Manager is installed.
Check if the proxy is configured in Machine/Browser for accessing the URL. If so, the same proxy settings must be configured in the Applications Manager. Click here for more info.
If the URL is authenticated, Then the necessary credentials has to be configured to monitor the URL.
If the URL requires any necessary headers or request parameters, Then it has to be configured correctly.
If the URL depends on User-Agent, Then the user-agent has to be configured for the URL monitor. Click here to get the User-Agent of your browser.
Troubleshooting:
A response code of 200 is expected by default. If any other response code is received, Click here to know the definition.
Reproduce the issue and share the latest Support Information File (SIF) from Applications Manager, with the "Print alllogs" option enabled. To do this, go to Settings > Logging, and choose "Print all logs".