Daniel,
I have gotten this working thanks to you.
The website referenced above is a Google Sites website. I don't have access to the <head> on any of the pages so am stuck with creating an XML file that defines a Google Gadget. It is a cumbersome work around where I need to use javascript within the XML to add javascript and CSS files to the head.
Below are the changes I made to my XML file to make this work.
I added this function
var includeMapEx = function(url) {
var link = document.createElement("link");
link.setAttribute("rel", "exhibit-extension");
link.setAttribute("type", "text/javascript");
link.setAttribute("data-ex-apikey", "AIzaSyBl3pTlyHYBW9TGNbsgt9bRqkA8zwHrJYY");
link.setAttribute("href", url);
head.appendChild(link);
};
It is called like this
instead of the way it was done before
I also changed all references to version 3.1.1 to STABLE
I did create the Maps API key but got a message that the Maps API was not enabled in Google Cloud Platform. Enabling that was the final step needed to make it work.