Auth popup window just says “0”

Hey, Postmatic Social Commenting 1.1.1 had been working fine for me for quite some time, but now when anyone clicks on any of the auth icons, the popup window just displays a “0” on a white background instead of the usual authorization stuff. Happens with all services.

I’m not sure when it broke, but probably recently, possibly after upgrading WordPress? Any suggestions?

I see that it is doing a redirect to e.g. https://www.facebook.com/dialog/oauth?response_type=code&client_id=…&redirect_uri=…pms-facebook-access-token&scope=user_about_me%2Cemail

and if I open that URL in my browser manually, it displays the correct FB icons and what not, and after I click, displays the blank “0” page.

The page I need help with: [log in to see the link]