Mirador - viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/82538/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-035707b2-1a03-4edd-8144-8c4e5b93bbb5",
      "cw-78f9b2c1-5076-4447-aeed-0e6376df3396"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-3c46459c-c8ba-4257-9dd9-bafd1866fd9b",
    "manifestId": "/api/digital_items/82538/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-78f9b2c1-5076-4447-aeed-0e6376df3396",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/82538/2/manifest.json/",
    "canvasIndex": 0
  }
}