For a remote session, you will need a Teltonika VIP Helpdesk account. For this, you will need to contact your Sales Manager. On the other hand, I can try to replicate your configuration on my devices to help you.
You need a public IP on the WAN interface of the OpenVPN server. Otherwise, you will not be able to establish the tunnel.
From what you explain in your configuration. It seems that you can access the RUT966 by IP of the OpenVPN server. Can you show me how you did the port forwarding configuration? Maybe there must be something wrong configured. Can you send me the updated troubleshooting file as well as the backup? This is to verify that the created interface is correctly connected.