Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/906/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-622bb18a-a8f9-497a-b36e-48b5647c8ba1",
      "cw-0946a939-12f4-46d5-adc6-e0d76dc15909"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e16aa720-1186-4ea9-b7e7-ddfad6c9f67c",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/906/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-0946a939-12f4-46d5-adc6-e0d76dc15909"
  }
}