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/900/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-d31b6847-3f53-46f1-bc91-6f58baa65043",
      "cw-5cb1dbe1-db87-4cb8-984a-0fb92d3867ab"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-72434482-54f1-4fee-b2dc-dc475140a785",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/900/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5cb1dbe1-db87-4cb8-984a-0fb92d3867ab"
  }
}