Hi, compliments for your plug-in :-) !!
I tried using "Demo Acceptance Checkbox", i copied your code
[acceptance accept-this-1] Check here if you accept these terms.
[acceptance accept-this-2 invert] Uncheck here if you accept these terms.
[acceptance accept-this-3 invert default:on] Uncheck here if you accept these terms.
[submit "Send"]
but there are problems
In your example demo the "send" button is not able to press without first checking the box to accept your terms, but in my blog the "send" button is always active (but the email not send) no error message appears
i have your plug-in CF7 3.3.3