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/maps1/4616/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-cc6a59fc-017b-4c02-9036-eefa82cf2378",
      "cw-ffc183ea-6d13-46a9-a4cc-e40f37161932"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-0f4ff5eb-3d95-4723-9c58-05cda47a2f97",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/4616/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-ffc183ea-6d13-46a9-a4cc-e40f37161932"
  }
}