The Access Token represents the permissions given to AdEspresso to manage your Ad Account. From time to time this permission expires and you will need to renew it in order to maintain the usual service of AdEspresso.
In order to keep using the platform, you need to renew permissions, and is super easy to do: you only need to visit the Ad Account page and click on the Renew it button.
You need to renew permissions with the same FB user you imported the Ad Account, if you do not recall which FB User gave permissions for that Ad Account, you only need to click on the ID just below the 'renew' button: you need to be logged as that user to renew the permissions.
The FB User section circled in red, when clicked, will direct you to the Facebook Account you need to be signed in to in order to renew the access token in your account.
Q. What happens if the Facebook user that has been connected to my AdEspresso account has left the company?
A. In this case, you will need to move the permissions of your ad accounts to a different Facebook user to keep your AdEspresso account working fine. There is a separate article for these situations, available here!
Q. What happens if my access token remains left expired?
A. You should renew your access token as soon as possible. If you leave it expired your campaign data will not be refreshed, changes made to your campaigns through AdEspresso will not be sent to Facebook, and you will not be able to create new campaigns from the AdEspresso platform. Your Access token allows the AdEspresso to function in all aspects and ignoring the expired access token warning on your account is a bad idea for any period of time.