If you are using Chrome, you should follow next steps:
Click on Settings, scroll to the bottom and click the Show Advanced Settings link.
Click on Open proxy settings.
Click the Security tab > Trusted Sites icon, then click Sites.
Enter the URL of your Trusted Site, then click Add.
Click Close > OK.
2. Click here to download the installer.Tip: Check if your Antivirus is not blocking the installation. You may need to deactivate it while installing the AddIn.
3. Open Excel and check if the AddIn has been installed.