Task-organized, copy-paste-ready FortiOS commands: curated from the field, not scraped from the docs. Speaks Cisco too: try show ip route.
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Paste the IPsec configuration from both ends and this compares them parameter by parameter: what must match, what must mirror, and what is only a local choice. Where a setting is absent it is read as the FortiOS default, so a show from one box and a show full-configuration from the other still compare correctly. When the far end is not a FortiGate, switch that column to enter parameters and fill in what the customer sent.
Side A
Run both of these and paste the output together.
Side B
Or switch to enter parameters if the far end is not a FortiGate.