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/619/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-acf81946-ac42-4fc8-8c24-14ffcd97b83a",
      "cw-2c334153-0038-416a-a9b5-90e3f3ae9094"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b3f3c33e-26a1-4eed-9276-c0373e59287a",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/619/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-2c334153-0038-416a-a9b5-90e3f3ae9094"
  }
}