Get Facebook Numeric ID.
This tool is also available with API version.
Test this API (JSON):
Make sure the Facebook URL are correct and valid:
Facebook Numeric ID is some random numberic for your Facebook account. This is created when you Sign Up for Facebook.
Some plugin like Yoast SEO allow you to access Facebook Insights for your site, you need to specify a Facebook Admin. This can be a user. If you have an app for your site, you could use that as well.