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/maps1/14637/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-8def92ad-3f86-40c0-a500-2c64709918eb",
      "cw-3339337c-0d42-4151-811c-cfbb2b3cbe97"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-819e957e-5319-48e1-98a5-f43c1cc35257",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/14637/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-3339337c-0d42-4151-811c-cfbb2b3cbe97"
  }
}