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/maps1/12623/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-85a7e2de-3009-45fd-827e-e719a06c8261",
      "cw-5d258731-4716-47a7-a2a7-325642cda794"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-37f8940b-3721-4063-bf7f-55ffb7943835",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/12623/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5d258731-4716-47a7-a2a7-325642cda794"
  }
}