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/b22w1jb97910.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-285f8b98-bfc1-4c95-95af-0212476cdc6b",
      "cw-fe44276d-b29e-4f08-a657-40d71072c9b2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b558b6e8-9ce7-4b7a-8ffd-c5baf88022a9",
    "manifestId": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b22w1jb97910.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-fe44276d-b29e-4f08-a657-40d71072c9b2",
    "loadedManifest": "https://iiif-collection.lib.uchicago.edu/object/ark:61001/b22w1jb97910.json",
    "canvasIndex": 2,
    "allowMaximize": false
  }
}