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_05291/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-962444bd-830d-489b-972b-c169f267b246",
      "cw-6adcf614-94cd-43f4-87f1-f9d23f3099f2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f021d3ba-82fb-43bb-8916-26266f6834bd",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_10P_05291/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6adcf614-94cd-43f4-87f1-f9d23f3099f2",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_10P_05291/manifest.json"
  }
}