Failed to execute 'postMessage' on 'DOMWindow': The target origin provided does not match the recipient window's origin ('null')

Make sure the target window that you (or Facebook) is posting a message to, has completed loading. Most of the times I've gotten this error were when an iframe I was sending messages to had failed to load.

Another reason this could be happening is if you are using an iframe that has the sandbox attribute and allow-same-origin isn't set e.g.:

// page.html
<iframe id="f" src="http://localhost:8000/iframe.html" sandbox="allow-scripts"></iframe>
<script type="text/javascript">
    var f = document.getElementById("f").contentWindow;
    // will throw exception
    f.postMessage("hello world!", 'http://localhost:8000');
</script>

// iframe.html
<script type="text/javascript">
    window.addEventListener("message", function(event) {
        console.log(event);
    }, false);
</script>

I haven't found a solution other than:

• add allow-same-origin to the sandbox (didn't want to do that)
• use f.postMessage("hello world!", '*');

To check whether the frame have been loaded, use onload function. Or put your main function in load: I recommend to use load when creating the iframe by js

 $('<iframe />', {
   src: url,
   id:  'receiver',
   frameborder: 1,
   load:function(){
     //put your code here, so that those code can be make sure to be run after the frame loaded
   }
   }).appendTo('body');