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_03774/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-e48a1f90-8a9f-4add-ac39-1d2ab520dc3d",
      "cw-c09a9e88-4a71-4549-b786-d0ed23e9dd55"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-8c865b5b-5a27-49b8-ab94-f54dfa2976e1",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_03774/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-c09a9e88-4a71-4549-b786-d0ed23e9dd55",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_03774/manifest.json"
  }
}