i’ve never used it.
it says “Secure browsing is not supported This application does not yet support secure browsing (HTTPS).”
it would be nice if you host it such that it allows https.
I’m not sure about what application you are talking about, but AFAIK it’s not application problem, but it is problem of all applications on FB. This is just my opinion and I do not know many applications there (while I do not used them), but all these applications requires HTTP.