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/maps1/13546/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-05ba705d-977b-44b4-b28b-14b7837dc4c9",
      "cw-9da5a17a-b704-4f5b-a51a-bbea310dfd3a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-28ee4abb-5b6a-4264-a6e9-8db9ea40f9e3",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/13546/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-9da5a17a-b704-4f5b-a51a-bbea310dfd3a"
  }
}