JSFiddle - React, Tailwind, and code Playground

by Rafa Ola

HTML

<input type="text" placeholder="Your personal message" id="valbox"></input>

<input type="text" class="input-text" name="billing_last_name" id="billing_last_name" placeholder="" value="">

JavaScript

window.onload = function(){
    document.getElementById('valbox').onchange = function(){
        document.getElementById('billing_last_name').value  = document.getElementById('valbox').value;   
    }
};