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_12536/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-1fa8187b-95e3-4141-b399-713e0a22d3d0",
      "cw-4a4841e9-f66d-4c08-89c2-84d1a7d77b14"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-eb86270c-1605-46f0-9a43-9774156a2322",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_12536/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-4a4841e9-f66d-4c08-89c2-84d1a7d77b14",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_12536/manifest.json"
  }
}