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/867/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-db70be53-a7b9-4461-91b9-4f132603e3c7",
      "cw-8fca0939-b532-4355-baf6-64e890064b46"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-89112ac1-d5d2-462b-b5b3-319e7263b1c4",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/867/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8fca0939-b532-4355-baf6-64e890064b46"
  }
}