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/maps1/6576/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ba959555-d3a8-4333-848e-268ba4c92773",
      "cw-53e283cb-470d-4147-870f-f59e21c420a1"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ec343c28-576a-4fe4-babd-a38336b7925d",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/6576/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-53e283cb-470d-4147-870f-f59e21c420a1"
  }
}