Adding an upstream port is one of the configuration steps that must be done in a self-managed instance to enable a secure pathway between a self-managed Jira Software instance and several Atlassian Cloud products. An upstream port is the port on your self-managed instance that receives traffic from the application tunnel. You need to configure the upstream port for each product that you want to connect to the tunnel.

Reference=Configure required connections and upstream portsandCreate an application tunnel to your self-managed instance