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/971/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-901a6613-5720-468a-a07b-173249b4b360",
      "cw-ab1fa4a1-7f04-43bf-be18-3244be0d0094"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-33aeb396-1167-4628-95ea-e92cc5b52dc4",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/971/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-ab1fa4a1-7f04-43bf-be18-3244be0d0094"
  }
}