If you are getting this error when updating the plugin. This is happening either because the license key is expired or it is not activated on the URL the extension is installed on.
You can resolve the Download Failed: Unauthorized problem by two ways:
1-A- Activate your License Key
You need to activate your license key. Go to Schema > Settings > Licenses in your Dashboard, and add it into the related license key field.
1-B- Manage your sites
Another way to resolve this problem is to manage your site within your account.
You can log into your account, click on the License Keys tab, then click on the Manage Sites link for the license key. From that page you will be able to add or remove URLs for the license. Once the proper URL is registered on the license key, you will be able to install the update.
2- Renew Your License Key
If your license key is expired, you can renew it within your account.