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/maps1/15030/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-1bd232c2-a852-4696-b50f-7c06bb368873",
      "cw-d2be2c90-d2da-4b27-b9da-673a7c7753c1"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-688ea833-d8c2-4104-ade4-dad431f6fe38",
    "manifestId": "https://digital.libraries.psu.edu/iiif/info/maps1/15030/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-d2be2c90-d2da-4b27-b9da-673a7c7753c1"
  }
}