Mirador viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/142283/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-433a189b-8971-4d5d-a491-63221f7fb34e",
      "cw-1163091b-38b9-4d57-91ff-375a891301e8"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-46e49ab8-1bf2-4f1c-85e6-9a36a13e380c",
    "manifestId": "/api/digital_items/142283/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-1163091b-38b9-4d57-91ff-375a891301e8",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/142283/2/manifest.json/",
    "canvasIndex": 0
  }
}