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/maps1/10957/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-49b23b4f-a187-4c69-b553-638b532d6c85",
      "cw-c7d0931e-f249-4bb7-b1df-24db764861b5"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-f24c60e3-92a1-45fc-97a9-63b801ad1336",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/10957/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-c7d0931e-f249-4bb7-b1df-24db764861b5"
  }
}