To create IPsec you have to fill in several columns on the IPsec page including:
Phase 1 - Remote VPN
VPN IP address on the destination project.
Phase 1 - Pre Shared Key
Keywords must be the same as the goal project.
Phase 2 - Remote Subnet
IP address of the subnet on the destination project
Here are the steps to create IPsec:
On the Network page, select the VPN tab, and select Configuration in the More column.
Select the IPsec tab and click the Create IPsec button.
In the Remote VPN section, fill in the IP address of the destination VPN project.
Press the Generate Pre-Shared Key button if you don't have a key yet, whereas if you already have the key from the target project, paste it into the Pre-Shared Key column.
Fill in Remote Subnet with the subnet IP address and prefix used in the destination project.
A notification appears "IPsec configuration [vpn-name] has been successfully created".