Error message if checkbox was not confirmed

Design help Layout & Design
1

Hi everbody,

got some question regarding forms and checkboxes:

Does anyone know, how it works, that I get an error message when all fields in the form have been filled in, but the checkbox has not been confirmed?

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

2

Hi, “Read-only” link doesn’t work. Can you fix this?