SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2cw3797p05h.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ffcf1139-b4e0-4607-a02d-dd8138e36721",
      "cw-405014dc-d90b-416c-b0cb-5754a04a5b05"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-60a191e7-3a42-4124-a304-4aa4b6c97d12",
    "manifestId": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2cw3797p05h.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-405014dc-d90b-416c-b0cb-5754a04a5b05",
    "loadedManifest": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b2cw3797p05h.json",
    "canvasIndex": 2,
    "allowMaximize": false
  }
}