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/960/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-faab3418-08fd-44db-bf54-fa3e65fd02d9",
      "cw-32b78b7c-e9e2-4e11-a8d3-4b3b76dbbdfa"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-3a2ceef2-ab2f-4bbc-8504-a9814b036ede",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/960/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-32b78b7c-e9e2-4e11-a8d3-4b3b76dbbdfa"
  }
}