A form doesn’t send anymore

Hello,

First, thank you for your great plugin !
Great job, we love to work with it 🙂

But since some days, we have a problem on this page :
https://www.batico.be/we-portes-ouvertes/

The form doesn’t send and we have an error. W
e have debug on, but no error messages.

We don’t know why suddenly it doesn’t send anymore. Can you help us ?
It’s very important.

Thank you,
Stephane

The page I need help with: [log in to see the link]