JSFiddle - React, Tailwind, and code Playground

HTML

<div>      
    <label for="confirm" class="fixedwidth">Yes I confirm all my details are correct</label>
    <input type="checkbox" name="confirm" id="confirm"/>
  </div>
  <div class="button">
    <input type="submit" value="SUBMIT" onclick="validate()" id="btnSubmit" disabled/>
  </div>

JavaScript

document.getElementById("confirm").onchange = function() {
    document.getElementById("btnSubmit").disabled = !this.checked ;
    
}