CF7 not working anymore outside WordPress

Hello, i have a wordpress site an 3 static pages, outside wordpress, where i initialized the wordpress environment to use wordpress plugins.
I needed that to load contact form 7 in the landing pages.

It worked ok, but after the last CF7 update, when i send a message to CF7 i don’t get the “Message sent” notification. The circular arrows keep spinning. The message is delivered but the visitor doesn’t know that and I had one client sending a message 8 times.

I used firebug and I noticed the response set back is not in json format, but is full html, starting with doctype declaration.

Inside the wordpress pages, the form works perfect. What changed in the latest version that made my setup not working??

Can you help me fix it?

Thanks!

https://wordpress.org/plugins/contact-form-7/