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/maps1/20047/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-94c0fd19-089e-4d6f-852f-21ea232687a0",
      "cw-7e05cdbe-a5d1-4fc2-8914-ed83375afab2"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-5104aacd-2eb4-43c6-832b-59122c59762c",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/20047/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-7e05cdbe-a5d1-4fc2-8914-ed83375afab2"
  }
}