Before starting the process, make sure that you are logged in to your Zendesk instance with the user account you wish to perform the action with.
To refresh/revalidate your Zendesk token, click on the cogwheel on your Unbabel app and click Account setup (you need to be at least a Portal Admin and you will be required to log in);
Go to Settings;
Click the three dots and select the option Refresh Token;
Please note that you must have both a Customer Portal Admin role (at least) and be a Zendesk Admin in order for the procedure to work as intended.
Note: Refreshing the Zendesk Token will determine that the user completing the process becomes the new Unbabel Admin.
And voilà, we are back in business.