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/maps1/13215/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-6d8293a6-f4af-4f06-a892-89f4239070a5",
      "cw-e856319b-3558-4a5f-8b88-4c6d4e17a070"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-aa5e0e26-a60a-4f95-9b79-bfbd918e742f",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/13215/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-e856319b-3558-4a5f-8b88-4c6d4e17a070"
  }
}