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/747/manifest.json",
    "isFetching": false
  },
  "window": {
    "collectionIndex": 0,
    "companionAreaOpen": true,
    "companionWindowIds": [
      "cw-28fce2ea-5402-4174-8916-749c126b096a",
      "cw-58cd9032-846f-4f76-aa7e-c0d9c29486bc"
    ],
    "draggingEnabled": true,
    "highlightAllAnnotations": false,
    "id": "window-b788ed85-e7c1-426b-baaf-2c38b320224e",
    "manifestId": "https://cdm16022.contentdm.oclc.org/iiif/info/mgs/747/manifest.json",
    "maximized": false,
    "rangeId": null,
    "rotation": null,
    "selectedAnnotations": {},
    "sideBarOpen": false,
    "sideBarPanel": "info",
    "thumbnailNavigationId": "cw-58cd9032-846f-4f76-aa7e-c0d9c29486bc"
  }
}