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/750/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-670ba649-0951-4011-9bd1-561179d23011",
      "cw-ffaebfd8-ece7-45a1-af34-e82139e6f254"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-5b069568-1cdf-451c-a542-a8a9d857c1ad",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/750/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-ffaebfd8-ece7-45a1-af34-e82139e6f254"
  }
}