When using the IKEv2 protocol, the Remote ID refers to the VPN server’s domain name or IP address, while the Local ID corresponds to your VPN account username.
Example:
If you connect to the server eu-fr.321inter.net, this same address should be entered as the Remote ID. The Local ID must match your VPN login name.
Take a look at this settings window in IOS:

Of course your username you have to replace by your real username and put in your VPN password.
About IKEv2
IKEv2 (Internet Key Exchange version 2) is a modern VPN protocol known for its strong security and excellent performance. It is especially well-suited for mobile devices thanks to its ability to automatically reconnect when switching networks or recovering from dropped connections, all while maintaining fast speeds and reliable encryption.