Mirador viewer

SyntaxError: Unexpected token '<', "<br />
<b>"... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<br />\n<b>\"... is not valid JSON",
    "id": "https://iiif.rbge.org.uk/herb/iiif/E00891611/manifest",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-3d18c0b3-6fda-4e97-8996-e4033b8b2ee2",
      "cw-8bdb90ce-6be7-40dc-9ac8-1de7ac43386a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b3eb8c24-c798-456d-956e-852160e5fab2",
    "manifestId": "https://iiif.rbge.org.uk/herb/iiif/E00891611/manifest",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8bdb90ce-6be7-40dc-9ac8-1de7ac43386a"
  }
}