Help! error!

2021-03-30 14:03:51.702 WARNING: [40] [hostname=localhost id=shard] MucClient.setPresenceExtensions#420: Cannot set presence extension: not connected.
2021-03-30 14:03:51.883 WARNING: [30] [hostname=localhost id=shard] MucClient.lambda$getConnectAndLoginCallable$7#588: [MucClient id=shard hostname=localhost] error connecting
org.jivesoftware.smack.XMPPException$StreamErrorException: host-unknown You can read more about the meaning of this stream error at http://xmpp.org/rfcs/rfc6120.html#streams-error-conditions
<stream:error><host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/><text>This server does not serve auth.ots.re.kr</text></stream:error>
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.parsePackets(XMPPTCPConnection.java:1059)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.access$300(XMPPTCPConnection.java:1000)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader$1.run(XMPPTCPConnection.java:1016)
        at java.lang.Thread.run(Thread.java:748)
2021-03-30 14:03:51.883 WARNING: [118] org.jivesoftware.smack.AbstractXMPPConnection.callConnectionClosedOnErrorListener: Connection XMPPTCPConnection[not-authenticated] (0) closed with error
org.jivesoftware.smack.XMPPException$StreamErrorException: host-unknown You can read more about the meaning of this stream error at http://xmpp.org/rfcs/rfc6120.html#streams-error-conditions
<stream:error><host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/><text>This server does not serve auth.ots.re.kr</text></stream:error>
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.parsePackets(XMPPTCPConnection.java:1064)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.access$300(XMPPTCPConnection.java:1000)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader$1.run(XMPPTCPConnection.java:1016)
        at java.lang.Thread.run(Thread.java:748)
2021-03-30 14:03:51.884 WARNING: [118] [hostname=localhost id=shard] MucClient$1.connectionClosedOnError#277: Closed on error:
org.jivesoftware.smack.XMPPException$StreamErrorException: host-unknown You can read more about the meaning of this stream error at http://xmpp.org/rfcs/rfc6120.html#streams-error-conditions
<stream:error><host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/><text>This server does not serve auth.ots.re.kr</text></stream:error>
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.parsePackets(XMPPTCPConnection.java:1064)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader.access$300(XMPPTCPConnection.java:1000)
        at org.jivesoftware.smack.tcp.XMPPTCPConnection$PacketReader$1.run(XMPPTCPConnection.java:1016)
        at java.lang.Thread.run(Thread.java:748)

After I accidentally deleted all the log folders, this error log was exported and it does not work. Help!

Seems there is no such virtual host configure in your prosody config.