Mirador - viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/127253/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-76449c16-fc23-4362-bf03-7694b0e58a11",
      "cw-8d6929ca-9f6a-4a5d-a843-b14c1baa7992"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-51ab83ba-5571-43ec-a4f8-a268c87cf153",
    "manifestId": "/api/digital_items/127253/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-8d6929ca-9f6a-4a5d-a843-b14c1baa7992",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/127253/2/manifest.json/",
    "canvasIndex": 0
  }
}