Problem sending the certificate along with request (MTLS)

We are trying to send a file to a partner via mendelson as2, but a 401 error occurs.
From the side of the partner, they answered that we are not sending the certificate along with request.
At Partner end, there no user and password for authentication and it is support certificate authentication only.
They sent the following information from the log:
{
"ssl_fc_has_sni": "1",
"ssl_mtls_used": "0",
"ssl_fc_sni": "test.ich4ls.net.sap",
"ssl_mtls_has_crt": "0",
"message_code": 401
}
Please tell me how to use MTLS in requests.

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