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/935/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-be62a334-e28a-430d-affc-9b37eb1206d3",
      "cw-5942ddee-b321-4eec-b9cf-2a5a551a7f54"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-18c6d94f-83f8-4359-9eba-c8284b5bd547",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/935/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-5942ddee-b321-4eec-b9cf-2a5a551a7f54"
  }
}