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/743/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-ea4cf169-d032-4dc6-b3c1-9791c80490d0",
      "cw-6226f7e3-0854-4a2a-baf2-0a8f378dab40"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-7d3aa79c-9ef7-4d90-a139-0faf770fbb27",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/743/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-6226f7e3-0854-4a2a-baf2-0a8f378dab40"
  }
}