First of all, let us clarify that it’s not strictly necessary to enter a Facebook App ID under SEO > Social > Facebook. Leaving this field empty won’t interfere with the ability to share posts on Facebook but may limit your ability to use Facebook features like Insights.
That being said, can you please make sure the Facebook App is in Live mode. If it’s in Development mode, Yoast SEO won’t be able to verify it and it will return a “The Facebook App ID you entered doesn’t exist” message.
Please manually check the app ID using the following URL replacing <APP_ID>
with your app ID.
https://graph.facebook.com/<APP_ID>
If it’s a valid app ID, it should show a category, link, name, and other APP relation information. If a manual verification shows a valid app ID, there is a communication issue somewhere between your site and Facebook.
If it’s not valid, it will display an error like this: “Unsupported get request. Object with ID ‘<the app id you checked>’ does not exist.” If the manual verification shows an error, the app ID is not valid according to Facebook. Please check the app ID again and/or contact Facebook to find out why you see it as valid but the verification returns an error.