Hi All; I bumped into this issue today and noticed that when I added the facebook page URL the page plugin code generator (https://developers.facebook.com/docs/plugins/page-plugin) I got the same error – This is on Meta’s developer site.
This made me assume it could be some stale cookies that are causing the issue – When I accessed the page again using incognito mode in chrome I was able to confirm this.
After deleting the Facebook cookies from my browser, it all worked again.
I hope that this helps!
