OpenVPN is an open source VPN daemon.

OpenVPN supports SSL/TLS security, ethernet bridging, TCP or UDP tunnel transport through proxies or NAT, support for dynamic IP addresses and DHCP,

OpenVPN supports conventional encryption using a pre-shared secret key (Static Key mode) or public key security (SSL/TLS mode) using client & server certificates. OpenVPN also supports non-encrypted TCP/UDP tunnels.

Errors

OpenVPN Site-to-Site Setup

Potential Advanced Settings you can try:

USE AES-128-GCM/AES-256-GCM!!!

auth-retry nointeract;
persist-key;
remote-cert-tls server;
reneg-sec 0;
auth-nocache;
fast-io;
sndbuf 524288;
rcvbuf 524288;