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_05173/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-3b01b864-9726-4954-866b-ee20a290afd2",
      "cw-7535932b-55df-421b-a6c4-ec69bd58e281"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f1d49243-3f54-4aba-a4b7-264494bf6186",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_05173/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7535932b-55df-421b-a6c4-ec69bd58e281",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_05173/manifest.json"
  }
}