Before you begin to set up RealVPN IKEv2 connection on your macOS computer, you need to get your VPN account credentials from the RealVPN's User Settings.
Sign in with your account at https://realvpn.io
Open the dropdown Account menu and click Settings.
In the opened window select the required VPN server you want to connect to.
Then select the IKEv2 protocol from the list.
Click Generate to get the connection data.
Now proceed to setting up the connection on your macOS computer.
On your Mac open System Preferences > Network.
Click + button to create a new service.
In the opened dialog select VPN as Interface, IKEv2 as VPN Type and input any name for this new VPN service, e.g. RealVPN.
Now input the Server Address from the connection data list which you have generated, use the same data for Remote ID, leave the Local ID empty and tick Show VPN status in menu bar checkbox.
Next click the Authentication Settings button and in the opened dialog use the generated connection data and fill Username and Password.
Click OK and then Apply. Now you have the VPN connection set.