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/680/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-7bd07ed8-68e2-4748-8ac5-b2c755140e03",
      "cw-34b8695d-aaf8-458b-b34c-2642fd4ba6db"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-27b1e717-2878-445a-949d-a8212f49a540",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/680/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-34b8695d-aaf8-458b-b34c-2642fd4ba6db"
  }
}