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/950/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-aa37dd6a-abb5-463a-b1fd-671f44943bdb",
      "cw-2fa11535-b305-438f-b61a-0dc57ae4dc6d"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b96b6342-1f9d-44b4-a04f-998cae48ca34",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/950/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-2fa11535-b305-438f-b61a-0dc57ae4dc6d"
  }
}