This are easy challenge, It give us client application that should be used to connect with the server for transferring message. If we try to execute it locally, we can see that if we input an text, it will displayed otherwise.

The client application was closed itself when i try to connecting with the remote address.

Then i try to execute strace with this client application while it connecting into server to seeing what happened.

Luckily, i got the flags from there xD.

FLAG = HTB{n0t_qu1t3_s0_0p4qu3}