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_15289/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-11a79e26-a92a-4184-9506-1d9d9dea6372",
      "cw-30d3bac7-4732-4373-b6f0-9ca3f4c01db2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0395bafd-a71c-4f3c-8448-feba25882eff",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_15289/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-30d3bac7-4732-4373-b6f0-9ca3f4c01db2",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_15289/manifest.json"
  }
}