Authentication Failure
Authentication failure occurs when the request to a resource is missing or has invalid credentials.
Check if URL requires authentication
Access the URL in an incognito/private window and check if any pop up asking for credentials is shown. Enter the username and password required to access the URL's resource in the private window. Ensure that you have provided the same credentials in the "Basic/NTLM Authentication" field in URL Monitor's edit monitor page.
You can also check if the URL needs credentials by accessing it using cURL/Wget. Ensure you do not provide credentials in the command. See if the response code is 401- this means the URL requires authentication.
On navigating to the URL in a browser, if a form is shown in which credentials have to be entered, then the URL most likely uses form-based authentication. In such cases, ensure that the URL monitor's "Form Submission Method" is POST and the corresponding payload containing the credentials is configured.
Form-based authentication will be similar to the Applications Manager's login page.
Check User-Agent
Certain servers are designed to fail authentication for requests originating from sources other than browsers. In such cases, edit the User-Agent of the URL monitor.
You can get your User-Agent's value from https://www.whatismybrowser.com/detect/what-is-my-user-agent. After entering the value in the edit monitor screen, update the URL monitor and poll the monitor a couple of times, and check.
Special Characters
In rare cases, the presence of special characters in the password may lead to incorrect encryption while storing in the Applications Manager's database. In such cases, create a password without any special characters and update the same in the URL monitor's edit monitor page, update the monitor, and check.