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_05211/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-7b610146-eb48-4327-90d6-1c9c8e9a9ce9",
      "cw-42de93fa-59e0-4049-901b-fa9d4bdac92a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-62aa7f9b-bbdf-4236-b474-6a9fbf46990e",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_05211/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-42de93fa-59e0-4049-901b-fa9d4bdac92a",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_05211/manifest.json"
  }
}