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/664/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-9c4d7c00-699f-4973-b908-3c8cb2bc4b13",
      "cw-668c9505-36fb-44d2-adc0-5ea0b13e7d52"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-eaf06e32-6e58-48a1-9031-072bfc007a5e",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/664/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-668c9505-36fb-44d2-adc0-5ea0b13e7d52"
  }
}