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/maps1/5052/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b0b3a832-a61d-4765-86ae-215a1f1b1002",
      "cw-708a6adf-9852-44bf-8dbc-ae4161651cc6"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-6b05d92f-2e8c-4a2d-9523-eda7547c68c1",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/5052/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-708a6adf-9852-44bf-8dbc-ae4161651cc6"
  }
}