Fast Secure Contact Form

I’m sure there is a very easy solution to this issue, but I just can’t figure it out.

Each time I test the contact forms on my site, they go through perfectly fine. However, I do not get the “Your message has been sent, thank you.” message. The form submits and returns back to the blank contact form without any confirmation. Any ideas?

Here is one of my forms: https://lewisandnatashawilkes.com/contact-us

Thanks.