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/639/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-b3f85a59-a264-4fe3-b341-0c57e4fb2c4f",
      "cw-80614c8d-2561-4c9e-9bab-25b616167fb5"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-d0cd7c0e-db80-4dba-829c-0b1eeef0768c",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/639/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-80614c8d-2561-4c9e-9bab-25b616167fb5"
  }
}