title: Set custom Wordpress REST-API URL
body: <p>I'm running an regular wordpress instance on an apache2 debian server. For the frontend im using an react spa with the REST-API of the wordpress backend.
  Now, i've changed the url of the frontend to separate it from the wordpress backend with</p>
  <pre><code>/** SITE SETTINGS
   */
  
  define('WP_HOME','https://frontend.foo.bar');
  define('WP_SITEURL','https://backend.foo.bar');
  </code></pre>
  <p>The problem is, that the rest api calls are now made from <strong>frontend.foo.bar/wp-json/...</strong> (for instance, when im trying to update an existing post, i've receive the message &quot;Updating failed. You are probably offline.&quot;)</p>
  <p>Is it possible to somehow modify the api domain?
  There is a <code>rest_url_prefix</code> but it changes only the part after the domain.
  Thanks in advance!</p>