If you are having trouble figuring out the inventory option setting then this post is for you.
To begin with, the inventory option comes from the WP Travel Utilities plugin. You can enable the inventory option from the individual trip from the tab “Inventory option“
This option is especially for tracking the number of seats being booked for a trip i.e if you book the trip then enabling this option will display the remaining seat.
Further, if you are willing to use your own custom pax rather then using trip pax then you can use an inventory option. This option also allows you to display the Soldout message or enquiry option if the seat is fully booked.
Note: This option works for a fixed departure only. In case of trip duration this option is not applied.
Also, since you can add multiple pricing for the same trip, you can have the seat count separately for a separate pricing option.