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/689/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-cf750e84-0f3c-4f43-a31c-c81fb2587331",
      "cw-4d6719c7-8caf-44e0-9696-c6f28367ef18"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0b920b4a-490f-44c0-a6f1-cc84e25ba21e",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/689/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-4d6719c7-8caf-44e0-9696-c6f28367ef18"
  }
}