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_01404/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ab298d25-6113-4beb-aeea-d03979625b8d",
      "cw-ea396b5b-a224-425b-98ac-59f0a1bf5d32"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-7ea49034-b4e3-476d-93c7-66c7ef10e744",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_01404/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-ea396b5b-a224-425b-98ac-59f0a1bf5d32",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_01404/manifest.json"
  }
}