The phase 1 interface explicitly configures IKEv2, so a compatible peer must support that IKE version. With mode-cfg disabled, the overlay interface is not automatically assigned an address using IKE mode configuration, and the required interface addressing must be configured. The exchange-interface-ip capability exchanges configured FortiGate IPsec interface addresses, enabling user-defined overlay addressing. It is a Fortinet-specific integration and should not be assumed to interoperate with any third-party IPsec peer. The source candidate key incorrectly includes general third-party compatibility as if every configured Fortinet-specific mechanism were interoperable. Reference: FortiOS 7.6 CLI Reference — vpn ipsec phase1-interface, ike-version, mode-cfg, exchange-interface-ip. An operational review should distinguish the rule that matches the traffic from the interface that is ultimately selected. Valid forwarding also depends on destination route eligibility, current member state and the applicable SLA or quality-selection algorithm. A diagnostic showing configured members alone is not conclusive evidence that all those members will carry a particular flow.