Why is my Facebook app in a Page Tab not appearing to non-admin users?

I have a Facebook app running in a Page Tab (the tab of a Facebook Page for an organi开发者_运维百科zation). The Page Tab URL (and Secure Page Tab URL) points to a URL on my own server which holds a PHP page that contains an iframe of a Google Calendar.

The app works perfectly fine when I open the Page using the admin account (both http and https). But when I open the Page using the user account of someone who has 'Liked' the Page, the app does not appear at all (both http and https). Any suggestions? Thank you.

Check if the app is in sandbox mode, in the Advanced section of the Settings here:

https://developers.facebook.com/apps

I believe that is the problem.

You may overlooked the "sandbox" setting that should be "disabled", this could be one explanation as per the answer above. If this have not answered to your question, than you may find another explanation here: http://developers.facebook.com/docs/appcenter/guidelines/

Basically, if your application doesn't do anything it will probably not be approved and it will not be visible to nobody, except you - the developer. There are other issues, like copyrighted infringement and so on... please read.

(Also, just in case you are interested, it should be installed by more than 30 times, I guess different persons, in order to be "searchable").