CHECKBOX RED

I put time ago the form contact 7 and worked perfectly.
It suddenly stopped working and I have not touched anything in wordpress, nor have I installed anything new…
It’s strange . I get to send the red box.
I tried with other mail and it does not work either. I actualiced the version, and I’ve disabled all plugins to see if there coflict and does not work either.
Please I need help.
The web is http://www.ameliatohabelleza.es/contacto-cita/

Thanks.

https://ww.wp.xz.cn/plugins/contact-form-7/