I got the same problem. I think this is related to the OAuth token that is expired, so if you can, you can ask a new one.
In my case, I saw a paypal smart button click, which seemed to work. Then a second one, 36 hours later from the same page. That second click triggered that error. I don't know what is the impact on the customer and if the smart button handle the OAuth token refresh and I would like to know.