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/4718/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-1aaaa0e4-834d-4231-9a29-f351fd9ed9bf",
      "cw-cfce5ee9-c562-4951-9c53-e918eace24d4"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-3a344904-142f-43d3-9530-f6c0b74b1c1f",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/4718/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-cfce5ee9-c562-4951-9c53-e918eace24d4"
  }
}