title: Rename API endpoint from .php to .json
body: <p>A service is trying to access my API by sending a GET request.</p>
  
  <p><em>https://oberlo.com/fetch_stock.json?sku=123&amp;shop=testshop.myshopify.com</em></p>
  
  <p>The REST API on Wordpress doesn't understand the .json extension.</p>
  
  <p>How do I respond to a a GET request ending in .json with PHP?</p>