I see this message in the Stunnel (client) logs during SSL handshake with the server

The server requires a client certificate which has been configured in the stunnel configuration.
The handshake is working fine but I was wondering what exactly does this line mean.

From what I found so far, seems like there is a way for the server to specify which CA's it will accept for the client certificate and it can specify them in the ClientCertificate request that it sends

This server doesnt send anything like that, so I am guessing that is the reason for this log line?
Can someone please confirm?
Btw, I see this line only when using TLSv1.3. When I restrict the client to TLSv1.2, I dont see this line.

thanks

LOG

Peer certificate required

TLS state (connect): before SSL initialization

Initializing application specific data for session authenticated

TLS state (connect): SSLv3/TLS write client hello

TLS state (connect): SSLv3/TLS read server hello

TLS state (connect): TLSv1.3 read encrypted extensions

Received trusted client CA list not found

TLS state (connect): SSLv3/TLS read server certificate request