404 error

I have a popup on my site with a contact form 7 connected to constant contact. when you submit, you land on page not found with this in the url: http://www.destroymyfat.com/&lang#wpcf7-f209-o1

I checked the code inspector but I see no errors.

I have this popup with a different form plugin and it does not give me any errors. Can you please direct me on where I can troubleshoot it? Everything looks correct on the setup end…

url of the form/popup: http://www.destroymyfat.com