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_12N_17050/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-51f8022a-0b09-4c19-848d-58035d17e4d9",
      "cw-909a8882-80dc-44cb-83db-a51b62bd79cc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-945a9544-51a6-456f-81f6-dfec4ee7ebcf",
    "manifestId": "https://iiif.participatory-archives.ch/SGV_12N_17050/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": true,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-909a8882-80dc-44cb-83db-a51b62bd79cc",
    "loadedManifest": "https://iiif.participatory-archives.ch/SGV_12N_17050/manifest.json"
  }
}