Won't work with WP 4.3.1 – "Please try after some time."

Your plugin looks simple and really interesting. Sadly there is currently no way to subscripe for the newsletter via the plugins widget.

I always get the message: “Please try after some time.”

Background Info:
My WP setup is on a subdomain wp.domain.de and installed in domain.de/wordpress.
there are several domains which carry the user to the sub domain from diffrent ways to type the name of the domain.

I got some problems with the login attempt from these other urls, so i tried both urls and no subscribe possible.

keep it going ??