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/1040/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-68be6bc3-b89d-4de0-aed8-6fecfac0cec9",
      "cw-d1c2abe7-76fb-45f0-a4f0-ef098f5cdc7a"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-9e2e5aaa-4f9c-45e5-aa5e-a378a02ccc25",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/1040/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-d1c2abe7-76fb-45f0-a4f0-ef098f5cdc7a"
  }
}