Contact Form did not send E-Mails

Hi,

i have an issue with sending any mails for my Fotoworkshop-Website.
Customers could not use the form like this: https://www.naturfotografie-kruse.de/fotoworkshops/fotoworkshop-kreative-pflanzenfotografie/

I get a red-boxed E-Mail Massage. I deactivated any Plugins, changed Cpatcha Versions (now honeypot is installed), but nothing helps.
I tested with Check EMail, and it works.

But there is still one form that works: https://www.naturfotografie-kruse.de/kontakt/
but unfortunately i could not see any difference exepct the amount of fields.

I would be very glad if you can help me, cause it is my business.

Best Wishes,

Helmut

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