The chat window is loading for me when I visit your site in Chrome, Firefox and Edge browsers and I don’t see that error message in the console (though I see a few Wordpress script errors in there). Is this still happening for you? If so which browser are you using?
These kinds of errors can sometimes occur if a page is slow to load or can be temporary.
I am getting a similar issue with the postMessageToIframe.js:14 Failed to execute ‘postMessage’ on ‘DOMWindow’: The target origin provided I dont see an issue with this one did it get resolved?