Mirador - viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/126245/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-1107ef42-5d9b-4419-b2b8-2382b2c42165",
      "cw-b62e391a-51fd-4a4f-921d-bb9ff2a4f8ef"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-27b640b9-78ca-49a6-9fc3-94816faa09c4",
    "manifestId": "/api/digital_items/126245/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-b62e391a-51fd-4a4f-921d-bb9ff2a4f8ef",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/126245/2/manifest.json/",
    "canvasIndex": 0
  }
}