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/663/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-05e4e289-a2ef-480d-a09b-a6254c932841",
      "cw-34869e41-679c-4928-bd3b-dcb35c476dcd"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-81dd8012-3bc8-42de-b29e-224575de7e76",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/663/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-34869e41-679c-4928-bd3b-dcb35c476dcd"
  }
}