Invalid input error

I’m getting the same issue this thread had
https://ww.wp.xz.cn/support/topic/error-invalid-input-when-all-fields-are-completed?replies=7

I see a possible issue is the names. These are the names I’m trying to RSVP:
Deanna Taylor
Evan Taylor
Dexter Taylor
Ripley Taylor
Jessie Taylor

please help!
The site I’m using is password protected…

https://ww.wp.xz.cn/plugins/rsvpmaker/