Ultimate Facebook API won't verify

Hi all,

I had UF installed, you guys fixed an issue for me and it was working fine - suddenly it's saying:

"Please, enter correct Facebook API settings and make sure Facebook app is public"

I have checked this several times. There's no spaces. App on Facebook Developer is public. The API and secret key are definitely correct.

I have:
disabled and re-enabled the app on FB dev
deactivated all other plugins
reverted to a default theme
setup another FB dev app and it won't accept the api/secret for that one either

I would truly appreciate your assistance with this matter, my last issue took a long time to solve and I'm on deadline now.

I have enabled support access and if necessary, Vaughan has administrator privileges to my FB app.

Many many thanks,
Elsie