How to find Facebook Page id
If you are admin of the page.
Open the page you want to show gallery from. Right next to the "Profile Photo" and "Timeline" there is "About" tab. Click on it.
On the bottom of that page, you have the page id.
If you are not admin, use this website to find your Facebook page id.
The page can't have age restrictions
- To check if everything is ok with your page, log out from Facebook ( or open private browsing ) and open the page link. If it displayed, then it is ok. If the page is not displayed or Facebook says it doesn't exist, then this page has age or other types of restrictions.
Go in your page settings and make sure age restrictions are set like this
The "Cover" and "Profile" photos will be hidden from the gallery.