That's strange. We've actually never seen that error before.
I would make sure that the Client ID and Client Secret that you've set in the JFBConnect backend > Configuration > LinkedIn tab matches a valid application in your
LinkedIn Developer Apps area
. Did the application get deleted at some point? Is there a typo in the ID or Secret?
If the application is still present and you said that you've set up the application according to our
LinkedIn application setup guide
, then could you attach screenshots of your application setup from the LinkedIn app area (just leave out any client secret as this is a public forum).
-Melissa