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/maps1/22559/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-8f69b8a9-1ebd-44ab-b8cf-a60fe3283a11",
      "cw-9b31af1e-47ed-469e-ba81-5f77f15840d2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-5e0f3d7c-a7fe-4016-bdab-fc014db0f555",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/22559/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-9b31af1e-47ed-469e-ba81-5f77f15840d2"
  }
}