Neagent or Network Extension Agent is required for the IKEv2 protocol based VPN app to work properly. By accepting pop-up permission requests, Neagent VPN can receive authentication information stored in the KeyChain system. Without this information, the macOS Network Extension cannot establish a VPN connection.
When you connect to a server with GOOSE VPN on macOS for the first time, you will be asked whether GOOSE VPN may configure connections via VPN. You then have to enter the password of the Mac itself as the password. You can then press 'Allow'.
When the VPN connection starts, you may be asked that Neagent wants to store confidential data in the keychain. This is a security measure of macOS that ensures that your GOOSE VPN login details are stored securely. If you choose 'Always Allow', you don't have to enter your macOS user password each time you connect.