Mirador viewer

SyntaxError: Unexpected token '<', "<!DOCTYPE "... is not valid JSON

{
  "manifest": {
    "error": "SyntaxError: Unexpected token '<', \"<!DOCTYPE \"... is not valid JSON",
    "id": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/838/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-15ae6e23-02e9-4fdb-b484-9cca99dcab1b",
      "cw-8dbcf032-ce96-4a77-936d-dbd05a630e15"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-bd6d2325-1d66-4cdb-b4d5-a1ac7880c85c",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/838/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-8dbcf032-ce96-4a77-936d-dbd05a630e15"
  }
}