schema.json

{
  "type": "object",
  "properties": {
    "user": {
      "description": "The user that is selecting her peers",
      "type": "object",
      "properties": {
        "firstName": {
          "type": "string"
        },
        "email": {
          "type": "string"
        },
        "timeZone": {
          "description":
            "The user's local timezone. Must be a name from the IANA time zone database.",
          "type": "string"
        },
        "invitationToken": {
          "type": ["string", "null"]
        }
      },
      "required": ["firstName", "email", "timeZone"]
    },
    "users": {
      "description": "An array of users",
      "type": "array",
      "items": { "$data": "user" }
    },
    "oneOf": [
      {"required": ["user"]},
      {"required": ["users"]}
    ]
  }
}