Facebook returns the "Unsupported get request" error when trying to do any one of the following:
1. If the page is in sandbox mode (testing mode). It will work if you are not in sandbox mode anymore.
2. When you try to access age or country restricted content, since you need to be logged into Facebook as a user in that location or age group in order to see the content.
3. If the page is flagged as related to alcohol, you need to be logged in as a user, who is old enough to see the page.
4. Setting restrictions (like contains alcohol/18+) does not allow you to access restricted pages. So you always need you need to be logged in as a user, who is old enough to see the page or who meets the criteria set for that page.
Unfortunately Facebook provides us with the same error in all the cases above and therefore we are unable to distinguish and provide you with more information. Please check your page settings or contact Facebook support for more info.