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/maps1/20343/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-6e60961d-bfd7-4270-9f1b-027f91ad923f",
      "cw-bbf1c6a8-29eb-43bd-96b5-3419b0b808d4"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-c0aa43f5-7c6b-4fcf-a496-ae1bc43f9aa5",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/20343/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-bbf1c6a8-29eb-43bd-96b5-3419b0b808d4"
  }
}