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/1023/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-aed0587d-7c36-4e87-b687-80046da65898",
      "cw-a5ec8a8d-5c85-4be9-936e-c9b335b048fc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-1465b47b-e971-41b4-93a6-44e36e447442",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1023/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a5ec8a8d-5c85-4be9-936e-c9b335b048fc"
  }
}