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_00779/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-a310c81e-da77-4168-96b4-44bcdfd8b12d",
      "cw-fdfafae0-6a0c-4492-8be9-75d34b1f9f88"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f68f0536-9f81-4a55-8ac1-0931a5fec552",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_00779/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-fdfafae0-6a0c-4492-8be9-75d34b1f9f88",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_00779/manifest.json"
  }
}