Facebook Troubleshooting - Error Validating Access Token
A Facebook access token validation error occurs when the token used to authenticate your Facebook account with third-party tools, like Statusbrew, becomes invalid because Facebook's security algorithms have flagged your account.
Although there are many reasons for this to happen, a few fairly common are:
Notice of copyright violation
Running inappropriate/flagged images or videos on a page
Running inappropriate/copyrighted content in ads
Suspicious account activity
Suspected compromised account
If the access token validation error message appears on your screen, the following are a few steps you can take to resolve the issue.
Delete browser history and cookies
Directly log into Facebook from that browser. If the issue is related to pages or ads, you may need to log into your Facebook Business Manager.
You should then be prompted through a few necessary steps that will re-authorize and unblock your account
If you face difficulty while performing the above actions, contact Facebook Support through the Facebook Help Center.