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/maps1/15000/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-e58edb67-38db-449b-b4cc-ad2680966a8f",
      "cw-651ed3ac-e730-4328-b810-6231e260df4b"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-e6a44840-5a97-4729-a725-cde0b658d524",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/15000/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-651ed3ac-e730-4328-b810-6231e260df4b"
  }
}