Why can't I create a ZDF account?

I tried to register with the ZDF Media Library. Unfortunately, I always get an error message at the end saying the email address is misspelled. But it's definitely correct.

The problem seems to be the hyphen in my email address. It consists of my last name and @web.de. My last name has a hyphen.

Without the hyphen, there was no error message and no confirmation email to my email address.

I tried it on my laptop and phone. Nothing worked.

What else can I do, or how can I contact ZDF? I can't find anything about this on the ZDF website.