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_12532/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-7d668e75-67ed-4e97-8f92-6f1ab7c68b2b",
      "cw-f8d685ed-88ba-4c0c-b6ac-534ea2485480"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-5dd8b368-3b45-46d1-b6ee-e94ef7cf7ccd",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_12532/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f8d685ed-88ba-4c0c-b6ac-534ea2485480",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_12532/manifest.json"
  }
}