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_07475/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-57898a92-e44a-448d-a2b2-ba5433052408",
      "cw-f2186021-62a3-420d-b649-1c6c6d84596a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-4eeed1dd-d8ba-46a7-90f3-8ab5d950ab81",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_07475/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f2186021-62a3-420d-b649-1c6c6d84596a",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_07475/manifest.json"
  }
}