Check an API URL for Errors
This is a basic test the end user can do when an API request fails from an application, why do you need to do this?, most of the time apps are configured with URL+API key to authenticate and fetch information, however, the app sometimes fails without giving a reasonable message to understand what is happening.
Open your browser tab in a private window.
The simple test you can do is open your browser and copy paste the URL+API key request and see the resultant message.
Here is an example screenshot

Also, you can use tools like curl, and Powershell, examples given below
https://www.baeldung.com/curl-rest
Also please check the “Computer Science degree“