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/781/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-c74feb4f-aaf1-4277-ab65-baf5c29340d0",
      "cw-66275f07-bc68-4a2b-9cf4-ec16faaa0f78"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-3f5506b4-1480-449d-981b-a9890342d5d5",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/781/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-66275f07-bc68-4a2b-9cf4-ec16faaa0f78"
  }
}