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/709/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b5a87502-6738-438d-b41f-110dc5bc7c87",
      "cw-fb3803e6-7c50-48b7-af23-c6d5bffdaa3f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b4bc643b-ca07-4ea8-91d6-200342a0a0e0",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/709/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-fb3803e6-7c50-48b7-af23-c6d5bffdaa3f"
  }
}