Mirador viewer

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

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https%3A%2F%2Ffotografia.cultura.gov.it%2Fpresentation%2FFB005685_13%2Fmanifest",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-c100a913-e683-428f-9afa-449c1fea4282",
      "cw-8dc914b4-b215-4dc1-8aca-e5f487ff753f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-8dfb1958-c6ab-4962-a270-ebaf2fa6c137",
    "manifestId": "https%3A%2F%2Ffotografia.cultura.gov.it%2Fpresentation%2FFB005685_13%2Fmanifest",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8dc914b4-b215-4dc1-8aca-e5f487ff753f",
    "loadedManifest": "https%3A%2F%2Ffotografia.cultura.gov.it%2Fpresentation%2FFB005685_13%2Fmanifest"
  }
}