Cannot set key of conference solution in manifest file

I cannot set "key" property in manifest file of GSuit application

"conferenceSolution": [{
    "onCreateFunction": "createConference",
    "id": "messanger",
    "name": "Some messanger",
    "key": {
      "type": "addOn"
    },
    "logoUrl": "https://logos.com/some/logo123.png"
  }]

but on push, I get error that: GaxiosError: "appsscript.json" has errors: Invalid manifest: unknown fields: [addOns.calendar.conferenceSolution[0].key] at Gaxios._request (C:\Users\iyano\AppData\Roaming\npm\node_modules\@google\clasp\node_modules\gaxios\build\src\gaxios.js:85:23) at processTicksAndRejections (internal/process/task_queues.js:93:5) at async OAuth2Client.requestAsync (C:\Users\iyano\AppData\Roaming\npm\node_modules\@google\clasp\node_modules\google-auth-library\build\src\auth\oauth2client.js:350:18)

Sample request of how to create an event with conference data in Apps Script:

function myFunction() {
  var calendarId = "primary";
  var resource = {
    "summary": "event with conference data",

    "end": {
      "date": "2020-04-10"
    },
    "start": {
      "date": "2020-04-10"
    },
     "conferenceData": {
      "createRequest": {
        "requestId": "123",

        "conferenceSolutionKey": {
          "type": "eventNamedHangout"
        }
      }
    }
  };
  var event=Calendar.Events.insert(resource, calendarId,{"conferenceDataVersion":"1"})
  Logger.log(event.id);
}

If it is for an Addon - I assume that type should be addOn instead of eventNamedHangout.