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_04288/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b9d730ab-b76c-4120-8bcb-20944f82ee61",
      "cw-9942366a-d9ed-4a27-bb7c-5b7e3a324a64"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2e6c6a2e-339d-428b-a41d-ddd3ae2b48eb",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_04288/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-9942366a-d9ed-4a27-bb7c-5b7e3a324a64",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_04288/manifest.json"
  }
}