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/753/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-8e274ad7-5a57-444b-a344-0a1a25dc479f",
      "cw-c86846e4-b61c-439b-8787-6a6f92148ce2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-47512ac7-67e9-4074-8877-99706460899d",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/753/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-c86846e4-b61c-439b-8787-6a6f92148ce2"
  }
}