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_03997/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-61fb96a8-9dbd-4081-9497-670c910a2adc",
      "cw-23f45c7f-febf-4620-a49b-cd9b5ab437b8"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-031fdd2d-ca42-4791-8f5e-f41934a6a419",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_03997/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-23f45c7f-febf-4620-a49b-cd9b5ab437b8",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_03997/manifest.json"
  }
}