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/907/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-e2aafbdb-c8e3-4cd2-9184-b603e5e9fe80",
      "cw-6490d9ae-3abc-46da-bc27-b9626a7ddc4a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-366a78e4-48a7-4df3-9ae2-8ac4399f59e6",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/907/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6490d9ae-3abc-46da-bc27-b9626a7ddc4a"
  }
}