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_11867/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-03b04f35-acd6-4dd9-bbe1-2d28932c06cd",
      "cw-377fb3ec-52d1-4cdf-b16c-8e1cd2e4f62c"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-68c512ef-8459-4fe8-bdce-6d3503a4a827",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_11867/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-377fb3ec-52d1-4cdf-b16c-8e1cd2e4f62c",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_11867/manifest.json"
  }
}