JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//code.jquery.com/jquery-1.11.2.min.js"></script>
<label>
    <input type="checkbox" name="agreement" class="agreement" id="agreement" onclick="checkboxed()"> I read all the information in the red box above and followed the instructions!
</label>
<br/>
<input disabled="disabled" type="submit" name="submit" class="send" id="send">

JavaScript

function checkboxed() {
    var agreement,send;
    agreement= document.getElementById('agreement');
    send = document.getElementById('send');
    if(agreement.checked == true) {
        send.disabled = false;        
    } else {
        send.disabled = true;   
    }
}