Metadefender Endpoint Testing Harness is available once a user is logged in to the Metadefender Endpoint Management Developers Portal - https://gears.opswat.com/developers/docs
The login for the developer portal is the same as your regular Metadefender Endpoint Management login.
In order to use the Testing Harness you have to authorize the Testing Harness app to access to your data. This is expected and for security reasons.
After that you are redirected to main page
On this page you select APIs from dropdown menu – make sure that you always select the latest API version – 2.1. And also make sure that you read the documentation for every given API - https://gears.opswat.com/developers/docs/cloud_api
For specifying parameters in the Testing Harness use the input field URL. After altering the URL click on the SEND button and you will get responses on the same page. See remaining screen shots.