Update: I found this out from a paid plugin:
If you have a Facebook page with a URL like this: https://www.facebook.com/your_page_name then the Page ID is just your_page_name. If your page URL is structured like this: https://www.facebook.com/pages/your_page_name/123654123654123 then the Page ID is actually the number at the end, so in this case 123654123654123.
I’ve tried the above instructions too, on a few pages, doesn’t work.
