Mirador viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "/api/digital_items/150038/2/manifest.json/",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a86a84cd-7837-483c-a141-fc87e5586ade",
      "cw-a6014630-a429-46ae-9792-7e75b9030268"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-a2ff3ae1-f159-49ae-a345-d935bc04923b",
    "manifestId": "/api/digital_items/150038/2/manifest.json/",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "annotations",
    "thumbnailNavigationId": "cw-a6014630-a429-46ae-9792-7e75b9030268",
    "thumbnailNavigationPosition": "off",
    "loadedManifest": "/api/digital_items/150038/2/manifest.json/",
    "canvasIndex": 0
  }
}