Mirador - viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/82554/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b588ad2b-317e-475b-811a-bc4778508796",
      "cw-46be3b3c-e04d-4f0d-a071-ba526d519287"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-8ee18dcb-cd4f-4dbd-a5d7-2d2a2e438362",
    "manifestId": "/api/digital_items/82554/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-46be3b3c-e04d-4f0d-a071-ba526d519287",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/82554/2/manifest.json/",
    "canvasIndex": 0
  }
}