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/735/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-93d29060-e17c-423d-a5bb-a4efb986648a",
      "cw-d5c0eed5-5bb9-4d98-bb5c-f85c522afd5b"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-7b01a05f-e4e4-4185-81b7-564ba606f477",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/735/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-d5c0eed5-5bb9-4d98-bb5c-f85c522afd5b"
  }
}