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/maps1/29723/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-bea0a89a-0f1e-4852-9c44-9c58d06356fc",
      "cw-ca05e5d5-46dd-4137-859e-73c6da3c87b4"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-089a9a47-f4bd-4fae-bed1-8dfb1c3d5404",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/29723/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-ca05e5d5-46dd-4137-859e-73c6da3c87b4"
  }
}