How does the access-control-allow-origin header affect the ability to embed an iFrame in a PHP page?

The access-control-allow-origin header controls which domains can access resources on a web page. If the header is not set to allow the domain where the iFrame is hosted, the browser will block the iFrame from being embedded in the PHP page. To solve this issue, you need to set the access-control-allow-origin header to allow the domain of the iFrame.

<?php
header("Access-Control-Allow-Origin: https://www.example.com");
?>