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/maps1/8448/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-db2dd39b-447a-4229-b9ba-75068bb37cdf",
      "cw-b3d136b9-1c95-408a-a952-42f133ce49c7"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-2303fcfc-1191-48d3-8cdb-432f859629dd",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/8448/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-b3d136b9-1c95-408a-a952-42f133ce49c7"
  }
}