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/637/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-01c8cc78-81f8-4855-9b53-b0f2070cea37",
      "cw-b9491447-f18c-41bc-ad71-7b03d25fce3c"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-53ed3cd0-9657-4de3-bd0e-b3a273cdbe25",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/637/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-b9491447-f18c-41bc-ad71-7b03d25fce3c"
  }
}