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_13495/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-59475394-67ee-4f4e-92e7-b6696ef0b8f2",
      "cw-0680de1a-6365-461d-a9a7-683a08cd0041"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-d457c090-5c8e-4f54-9741-d1814dacf12f",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_13495/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-0680de1a-6365-461d-a9a7-683a08cd0041",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_13495/manifest.json"
  }
}