Mirador - viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/139147/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b5822b2a-7e5f-4596-99c6-c2b96c76ddf5",
      "cw-512b6b02-d084-4d22-b8f7-f2867c7a8d7e"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-54074fc1-ac7a-48b3-bdfb-99f1c7347459",
    "manifestId": "/api/digital_items/139147/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-512b6b02-d084-4d22-b8f7-f2867c7a8d7e",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/139147/2/manifest.json/",
    "canvasIndex": 0
  }
}