Cannot run Core.EmbedJavascript.HeaderFooter sample. Request Failed Access Denied

I am trying to run the https://dev.office.com/patterns-and-practices-detail/5837 sample in a Modern Communication site, but am getting an Permissions error. I am running this as a global admin, that is also a site collection admin. I have verified the app has full control for Web and Site collection. What am I missing?

EDIT: Looks like UserCustomActions are gone in new communication sites. Does anyone know how I can get a header/footer on the new communication sites? I cant really wait for the hub sites feature...