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/maps1/2415/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-c07dd839-2317-4a6c-b61e-73f3ad8bce66",
      "cw-a4c5ab4b-ced2-47d5-86e9-6cf1042e5b93"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-ad6f6359-10c6-43ca-ac6b-5b1e932dbab5",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/2415/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a4c5ab4b-ced2-47d5-86e9-6cf1042e5b93"
  }
}