You may encounter an error while trying to connect or refresh your LinkedIn account.
This error is rare, but can have the following causes:
Changing in your LinkedIn password
Adding 2-factor authentication to your LinkedIn account
Changing your privacy settings on your LinkedIn account
Invalidated LinkedIn tokens
The Fix
The error can usually be fixed by reconnecting your LinkedIn account.
If this doesn't work, do the following:
Go to LinkedIn Permitted Services and remove Post Planner
Then re-connect your LinkedIn account in Settings > Social Networks