Download Failed: Unauthorized
There are 2 main reasons why you see this error when trying to update the Pro plugin.
If your license key is expired, you will need to renew it before you can install the update. The status of your license key will be shown on the License Keys tab of your account page.
Please, read this article for more information.
License Key is not activated on the URL
This is happening because the license key is not activated on the URL the plugin is installed on. This can sometimes happen if you install the plugin and activate the license key on a temporary URL and then update the site to the final URL.
To resolve the problem, 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.