GNULS Client-Server client-server authentication error

I am using two example examples given by gnutls:

• "Simple example client with X.509 certificate support" without any changes.

• "Echo Server with X.509 Authentication". I have created a private key "key.pem" using certtool and a self-signed certificate "cert.pem" and will use it in this example.

  The server is working correctly ... the output is as follows:

  The server is ready. Listening to port "5556"

But if I run the example client, it returns the following error:

Handshake failed GnuTLS error: TLS connection was terminated incorrectly

and the server returns:

connection to 127.0.0.1, port 58587 Acknowledgment failed (request is invalid.)

What is the problem? Do I need to change the client example? If not, how can I check the TLS handshake process and the data sent between the client and server?