You can add any public company page, such as https://www.facebook.com/Coca-Cola/ It is not possible to add any personal Facebook account.
You can add any Twitter handle such as https://twitter.com/CocaCola?lang=de
You can add any YouTube account such as https://www.youtube.com/user/cocacola/featured
You can add any business Instagram account, such as https://www.instagram.com/cocacola/?hl=de It is not possible to add personal accounts.
You can add any company, school or showcase type LinkedIn accounts. It is not possible to add personal accounts.
If you are adding one of the above types of pages and you are still running into issues, please contact firstname.lastname@example.org.