Embed iframe not performing as expected

Using the share functionality in Mirador, I embedded <iframe src="http://dlg-staging.galib.uga.edu/record/dlg_sanb_thomasville-1920/presentation/manifest.json&maxheight=420" title="Image viewer" width="560" height="420" allowfullscreen frameborder="0"></iframe> into a google site.

No image appears. See https://sites.google.com/view/dlg-docs/mirador-viewer-embed-example