Error message when trying to load facebook registration iframe

I’m not sure if this topic is relevant to this forum but I figured enough of you PHP coders are familiar with integrating Facebook to you sites. I’m new to using Facebook APIs and I’m tying to load the user registration iframe from facebook onto my my site. But I get the following error every time I load the page:

Unable to load the registration form for XXXX. You may have previously blocked this app on Facebook. Go to your Facebook privacy settings to unblock this app. (Error: That ‘redirect_uri’ isn’t allowed for that client_id.)

I’m not sure what I didn’t do correctly. I setup my facebook app Id and here is a screenshot from the setup page

And here is how I configured the iframe: I replaced my app Id with 1111111111 for obvious reasons

<iframe name = "fb_signup" src="
             client_id=	111111111111&

Also tried the facebook XML but neither got an error message nor the pre-filled dialog from facebook

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