DOMException: Failed to execute 'postMessage' on 'Window' on report.applyTheme()

Good day! I am trying to build in a day/night switch into my Power BI Embedded app that will flip from dark to light. I want to extend the functionality into the embedded report itself. Here is the code:

  var report = powerbi.embed(reportContainer, config);
                           $.ajaxSetup({
                                async: false
                            });
                           var themeJson=  (theme == "material") ? $.getJSON("Content/power-bi-themes/light.json") : $.getJSON("Content/power-bi-themes/dark.json");
                            $.ajaxSetup({
                                async: true
                            });


                            report.applyTheme({themeJson:themeJson});

The error I am getting is in the subject line. Please help! 🙂