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/883/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-c7f8f7a5-09d5-4aa6-beb4-ff8935aa1d97",
      "cw-1369a70e-441c-4708-a9b6-eb53fb9596bd"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f7cf086c-5317-4be1-a88a-3723e9e45b5e",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/883/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-1369a70e-441c-4708-a9b6-eb53fb9596bd"
  }
}