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/maps1/7562/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-565c0a58-9fa7-4534-b269-48e0aef0dbe1",
      "cw-a5b6e47b-56f1-4cdc-95f2-d875b12aa86e"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-3c9dff71-86b6-493e-b6b1-ff72f8a19cef",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/7562/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-a5b6e47b-56f1-4cdc-95f2-d875b12aa86e"
  }
}