I try to use the Credits API on external site and get the following error in popup:
*API Error Code: 1151
API Error Description: Sorry, but this app may not be eligible to accept Facebook Credits. If this app has accepted credits before, please try again.
Error Message: Invalid Application*
As mentioned here:
only FB canvas applications are eligible for this.
BUT!
If I take the popup URL and change the display parameter from popup to page, it works fine.
So, I'm wondering, can I use it on external sites or not?
Why does it work as page and doesn't work as popup?
Why does it work as page and doesn't work as popup?
Because it's explicitly designed that way, as the documentation clearly mentions:
This dialog only supports desktop display modes: page. (https://developers.facebook.com/docs/reference/dialogs/pay/)
And https://developers.facebook.com/docs/credits/ also very clearly states,
Facebook offers a payments platform that enables developers to leverage our payments services to charge their users on Apps on Facebook as well as their Mobile web Applications.