The Token allows a connection between CCP and eBay's API. Without the token there would no connection and as such here is how to add or renew an eBay token within CCP.

Cloud Commerce Pro will always attempt to warn you in advance of your Ebay token expiring, allowing you time to generate a new one before the service is interrupted.

Admin → Configuration → Selling → eBay → Accounts

Select the Get Token button

This will prompt you to log in to your eBay account

Now that you are logged in, you will have to accept the T&C's agreeing to allow CCP and eBay to communicate.
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Once this is complete repeat the process for the OAUTH Token

When you are done head back to CCP and from the accounts screen, re-enable your channels