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_01409/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-68e7b3ef-a215-433b-8a74-c4a9e66a3ad0",
      "cw-f1dccab3-39bf-4c66-9003-bc6c2c2e88c6"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-4b757210-2aa0-4e3c-8d64-59b8e4f4dcba",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12P_01409/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f1dccab3-39bf-4c66-9003-bc6c2c2e88c6",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12P_01409/manifest.json"
  }
}