Trying to make a secure handshake between server and client with OpenSSL - c++

Question

I'm trying to make a basic Client-Server program that can exchange messages using the OpenSSL library. I'm very new to OpenSSL and cryptography and I'm trying to understand exactly how to make sure that the connection between my client and server is secure. Currently I'm using self signed certificates for both client and server but the certificate verification fails when the client tries to connect to the server with this error:
140336190395008:error:1417C086:SSL routines:tls_process_client_certificate:certificate verify failed:../ssl/statem/statem_srvr.c:3711:
In the main method of my server program, I first set verify for the CTX and use the following flags:
SSL_CTX_set_verify(ctx, SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT, NULL);
Then when setting up the servlet I call the following method to show certificates:
void ShowCerts(SSL* ssl) /*show the ceritficates to client and match them*/ {
X509 *cert;
long int verify;
char *line;
cert = SSL_get_peer_certificate(ssl); /* Get certificates (if available) */
verify = SSL_get_verify_result(ssl);
if (verify == X509_V_OK) {
printf("Yay it worked\n");
}
if ( cert != NULL ) {
printf("Server certificates:\n");
line = X509_NAME_oneline(X509_get_subject_name(cert), 0, 0);
printf("Server: %s\n", line); /*server certifcates*/
free(line);
line = X509_NAME_oneline(X509_get_issuer_name(cert), 0, 0);
printf("client: %s\n", line); /*client certificates*/
free(line);
X509_free(cert);
} else {
printf("No certificates.\n");
}
}
As I said I'm very new to this so I might be missing something basic here. Also apologies in advance if I missed any important info, this is my first time asking a question here.