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_01405/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-d3356d6d-379e-4437-b1d6-39ba79567887",
      "cw-99ee425f-126f-4966-bf61-3d027d5a25e9"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-c400503d-eb4f-4e76-b0f5-5b9e9be3f347",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_01405/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-99ee425f-126f-4966-bf61-3d027d5a25e9",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_01405/manifest.json"
  }
}