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/maps1/27454/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-74bf2a50-54cd-480e-b2a2-101d5b96672e",
      "cw-8f5fd43e-56ed-4122-8940-b201a7b83fd4"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-a4273aaf-4967-4216-967b-ee0346c12bc8",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/27454/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8f5fd43e-56ed-4122-8940-b201a7b83fd4"
  }
}