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_10P_00053/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-5c6497cc-b333-4167-86c7-06be06d279e3",
      "cw-be542d18-7efa-4b40-8b6e-d01d4d98bc1f"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e0500dfc-9a21-4142-98cd-4588616748f0",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_00053/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-be542d18-7efa-4b40-8b6e-d01d4d98bc1f",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_00053/manifest.json"
  }
}