Problem with SSL connection TCP socket Server python / Client C# in Unity

Hi everyone ! I try to connect my python's server and C# client in my unity project using SSL certificates. I have a python server and a C# client, using TCP socket and SSL to communicate, with my self-signed certificates. When i run my python app on my mac OS LAPTOP and my client on my windows LAPTOP, everything works, certificates check are ok connection is securised and i can communicate etc... But when i try to just copy and paste the C# client on unity and then lunch it, unity drop me this error : TlsException: Invalid certificate received from server. Mono.security.Protocl.Tls.Handshake.Client.TlsServerCertificate.validateCertificates (Mono.Security.X509,X509CertificateCollection certificates)

Here's my python server :

And here my C# client :

I insist on the fact that this client/server out of Unity works perfectly ( so its not a problem of certificates / key or password or format), but when i past exactly then client's code in unity and execute it, i have the unity error. I've heared about import CA root on mono etc... tried it but still not works, and i dont need any CA root on local computer because i did nothing like that when i ran the client out of unity and it worked. Waiting for your answer i'm stuck for 4 days already, sorry for my bad english. Thanks. Note : I'm limited to 2 pictures on the post, so you dont have the "main" to lunch the client in unity. Note : i tried on unity 2017.1.0f3, 2017.3.0f3 and 2018.1.2f1