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/1021/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-d37cded5-d49f-4297-a192-d444f7808026",
      "cw-a01ecaa8-6f0c-4c98-85fc-a1183406bd98"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-a1a14e6f-551e-47b0-83bf-21129e994b9b",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1021/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a01ecaa8-6f0c-4c98-85fc-a1183406bd98"
  }
}