Mirador viewer

SyntaxError: Unexpected token 'E', "Error from"... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token 'E', \"Error from\"... is not valid JSON",
    "id": "https://iiif.participatory-archives.ch/SGV_12P_09961/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-1906c307-985d-4a13-9b76-988413052529",
      "cw-10e36159-1e19-4e8f-8ed8-e5882c521a0d"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f4a4cd3e-c215-4f99-9ecb-1ddd26d79354",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_09961/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-10e36159-1e19-4e8f-8ed8-e5882c521a0d",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_09961/manifest.json"
  }
}