Hello sirs.
I have verified both supported Key Exchange Methods in the server and client using "ssh -Q kex" command
and found that they the same methods .
But still I'm encountering the issue below.

Code
using(SftpClient client = new SftpClient( "hostname", "username" , "password")){
client.Connect();
}

Stack Trace
Key exchange negotiation failed.
at Renci.SshNet.Security.KeyExchange.Finish() + 0x71
at Renci.SshNet.Security.KeyExchangeECCurve25519.Finish() + 0xe
at Renci.SshNet.Security.KeyExchangeECCurve25519.Session_KeyExchangeEcdhReplyMessageReceived(Object, MessageEventArgs`1) + 0x3f
at Renci.SshNet.Session.OnKeyExchangeEcdhReplyMessageReceived(KeyExchangeEcdhReplyMessage) + 0x60
at Renci.SshNet.Messages.Transport.KeyExchangeEcdhReplyMessage.Process(Session) + 0x14
at Renci.SshNet.Session.MessageListener() + 0x53
at Renci.SshNet.Session.WaitOnHandle(WaitHandle, TimeSpan) + 0x100
at Renci.SshNet.Session.WaitOnHandle(WaitHandle) + 0x16
at Renci.SshNet.Session.Connect() + 0x2d7
at Renci.SshNet.BaseClient.CreateAndConnectSession() + 0x12c
at Renci.SshNet.BaseClient.Connect() + 0x9b