Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://digital.libraries.psu.edu/iiif/info/maps1/22594/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-4fcb5d58-324a-4911-a343-ed38faf2aa17",
      "cw-bd91d6ef-4192-438d-86f6-f5fdf8595e40"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-bd797f97-8970-4222-b7e8-7d42a8c350b6",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/22594/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-bd91d6ef-4192-438d-86f6-f5fdf8595e40"
  }
}