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_00021/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-5f0d35e5-fa6f-4e0a-85da-59a630d8af5e",
      "cw-2a914cca-0681-440c-acc2-8ac3a317d083"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-833bb39c-bd95-4c23-b997-4f9c0c908ce5",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_00021/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-2a914cca-0681-440c-acc2-8ac3a317d083",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_00021/manifest.json"
  }
}