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/618/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-12aa3138-8eeb-4fb7-ad70-3f3bf0c5c9ff",
      "cw-79fb472e-f41f-45bb-95e1-ddac7fb810cc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-6fec0c58-5bdc-4939-900a-d090cdb64e83",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/618/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-79fb472e-f41f-45bb-95e1-ddac7fb810cc"
  }
}