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/772/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-9086ac8b-0c5c-4585-b7bd-baa2e2830a0b",
      "cw-f5f3f23a-1aa0-4ee9-8b2b-7ff220e2aa66"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-71284aa7-ec64-4b37-a333-01d52e68d07e",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/772/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-f5f3f23a-1aa0-4ee9-8b2b-7ff220e2aa66"
  }
}