The terms and conditions checkbox blocks the order even when ticked, why?

That is a validation bug. The terms field is either rendered twice (once by the Block and once by a plugin), bound to the wrong element, or its JS validation never re-reads the checked state. The result is a stubborn “Please read and accept the terms and conditions” error. We de-duplicate the field, fix the validation binding, and confirm a real order goes through with the box ticked.