如何通过Postman调用SignalR事件？尝试现有方案后仍报错

尝试通过Postman调用SignalR事件，已查阅Stack Overflow相关问题但未解决，调用时出现如下错误（示例URL已替换为myUrl）：

对应的C#实现代码如下：

private HubConnection hubConnection;
private IHubProxy hubProxy;

hubConnection = new HubConnection(myUrl, useDefaultUrl: false);
hubConnection.TransportConnectTimeout = new TimeSpan(10000);
hubConnection.Credentials = CredentialCache.DefaultCredentials;
hubConnection.Closed += _hubConnection_Closed;
hubConnection.Error += _hubConnection_Error;

hubProxy = hubConnection.CreateHubProxy(myHubName);
hubProxy.On<CurrencyPair>("getItems", value =>
{
    DoSomething(value);
}

使用的Postman版本：9.31.9

内容的提问来源于stack exchange，提问作者Vivek Nuna