All the updated iOS versions have IKEv2 protocol for VPN connection, follow the below steps to configure VPN on your iPhone or iPad using IKEv2
Click on Settings to open the settings menu and click on General, under General you will find the VPN option
Click "Add VPN Configuration"
The type selected should be IKEv2 and following details needs to be added:
Description: Name of your choice
Server: The server address that you wish to connect to. Refer http://network.limevpn.com/ for the server list
External ID: The same server address that was mentioned under "Server"
NOTE: In older iOS versions, you might see "Remote ID" instead of "External ID"
Local ID: Leave it blank
User Authentication: Username
Username: LimeVPN Username
Password: LimeVPN Password
After adding all the details, click on Done
Under VPN Configurations, to connect, click on the radio button besides the VPN profile that was created.