Error with Proxy

[ACZERWIN61]

net Core 8 MVC application When Is added proxy there is error - probably should not possible to use Proxy and DefaultProxy true

I make the some console test
var transport = new HttpsTransportBindingElement();

if (!string.IsNullOrEmpty(ProxyAddress))
{
transport.ProxyAddress = new Uri(ProxyAddress);
transport.UseDefaultWebProxy = false;
Console.WriteLine($"Proxy ustawiony na: {ProxyAddress}");
}
else
{
Console.WriteLine("Proxy nie jest ustawiony.");
}

var customBinding = new CustomBinding(encoding, transport);
_gusServices.Endpoint.Binding = customBinding;

[ACZERWIN61]

without proxy is working fine but when I add proxy receive the error
var proxyAddress = new Uri(proxyAddressValue);

builder.Services.AddGusClient(c =>
{
c.Environment = GusEnironment.Production;
c.Key = birKey;
c.ProxyAddress = proxyAddress;

});