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/823/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a325c654-6cad-4a97-bb99-86901c846d47",
      "cw-a023ce17-5571-4db6-a865-8515bde57570"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0c58ff6a-46b3-4e06-a0f8-a9573af2a012",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/823/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a023ce17-5571-4db6-a865-8515bde57570"
  }
}