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/maps1/8298/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-25d5e4d4-a091-4dd5-8cb1-77be16b4498f",
      "cw-7b66e155-56ea-49ed-b30d-ae47c34f9477"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-215ee8ee-30d1-4e93-a538-524328b5b3a9",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/8298/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7b66e155-56ea-49ed-b30d-ae47c34f9477"
  }
}