Troubleshooting steps: If any other activator was used to activate IDM previously then make sure to properly uninstall it with that same activator (if there is an option), this is especially important if any registry / firewall block method was used.
Uninstall the IDM from control panel.
Make sure the latest original IDM setup is used for the installation, you can download it from https://www.internetdownloadmanager.com/download.html
Now install the IDM and use the activate option in this script and if failed then,
Disable windows firewall with the script option, this help in case of leftover entries of previously used activator (some file patch method also creates firewall entries).
Some security programs may block this script, this is false-positive, as long as you downloaded the file from original post, temporary suspend Antivirus realtime protection, or exclude the downloaded file/extracted folder from scanning.