In this article, you will learn about the troubleshooting tips that you can try to solve the issue referring to the activation of the HEIMDAL license key. 
1. ENTERPRISE customers
2. HOME customers
ENTERPRISE customers
This issue can occur in multiple scenarios. Below, we will discuss each scenario:
1. Your Firewall/Proxy/VPN is blocking the connection between the HEIMDAL Agent and our servers
Make sure you whitelist/exclude the IPs, Ports and processes described in the System Requirements and Firewall Exceptions support article.
2. Windows Management Instrumentation (WMI) service
The HEIMDAL Agent is completely dependent on the Windows Management Instrumentation (WMI) service. WMI detects all active network adapters on the specified computer so it can then add the localhost IP Address, after that, the HEIMDAL Agent will start to filter your internet traffic.
3. Time and Date
This behavior can occur if the time or date is not synchronized between your computer and the domain to which you are attempting to log on. You can check and synchronize the computer time with your Domain Controller time using the command-line in an elevated Command-Prompt:
net time /set /y or w32tm /resync
The HEIMDAL Agent also depends on Windows Time service. Without it, the HEIMDLA Agent cannot communicate with the Domain Controller time anymore, so it will fail to activate the license key.
Solutions
If you don't have the required .NET Framework, you need to download and install .NET Framework version 4.6.1 or above (download link).
In case the .NET Framework libraries are corrupted (you get a .NET framework error in Event Viewer) you need to repair them for the HEIMDAL Agent to work properly by using this tool (Download it here). Or you can upgrade to the latest .NET framework version which is compatible with your Windows operating system (please check this documentation).
HOME customers
Solutions:
- Check your internet connection and make sure you can access the web.
- Open Date and Time by clicking the Start button, click Control Panel, click Clock, Language, and Region, and then click Date and Time
- Click the Internet Time tab, and then click Change settings. ...
- Click the Update now button
- It is very important to wait for the confirmation message that tells you the update was successful
If you receive an error confirmation message, please repeat the process until you receive the message that announces you the update was successful.
IMPORTANT
Please make sure the HEIMDAL license key was not already activated on more devices/computers than specified on your subscription. If it was activated on more (new computer or hard drive, a reinstall of Windows) devices/computers then please contact us using the Submit a Request option to revoke the HEIMDAL license key from the devices/computers that were decommissioned.