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_01861/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-4a188c4e-c059-4c04-8013-82620160108c",
      "cw-4a665b2a-727c-496e-b735-101e5228d489"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-86c09e67-681e-442f-a201-2cf3a3fabbe6",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_01861/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-4a665b2a-727c-496e-b735-101e5228d489",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_01861/manifest.json"
  }
}