The app ID specified within the "fb:app_id" meta tag was invalid

To link Domain Insights to an app rather than a user, you need to use the fb:app_id tag:

<meta property="fb:app_id" content="your_app_id" />

Source: https://developers.facebook.com/docs/insights/

Only personal IDs are allowed in the fb:admins meta tag. Application IDs won't work, even though they are actually valid (in contrary to what the error message says).

Optionally, it may also work with page_id:

<meta property="fb:page_id" content="395450240451647" />

The suggested app_iddidn't work at all :(

You have to make public you app to start works.