Assets → Accessories.
Give each one a name, a price, and whether it is charged per day or as a flat amount. Per day for a child seat; flat for an airport drop.
The one that catches people out
Leave the Vehicles field empty.
An empty Vehicles field means "every vehicle" and is what you almost always want. If you pin an extra to specific vehicles, it is only offered when every currently available vehicle in the group can carry it — because the customer books a group, and Glovebox cannot promise an accessory that only some of the cars have.
The trap is that pinning is usually accidental, and the failure is silent: the extra simply does not appear on your booking page, with no warning and no note. Worse, it flickers — as cars go out on hire and come back, the set of available vehicles changes, so a partially-pinned extra appears and disappears without you touching anything.
If an extra is missing from your booking page, clear the Vehicles field first. Glovebox flags extras in this state on the list with a warning, so check there too.
If it did not work
- The extra is not on the booking page. Clear the Vehicles field. This is the cause the overwhelming majority of the time.
- It appears for some dates and not others. The same cause: availability is changing which vehicles are in the set.
- It shows the wrong price. Check per-day versus flat — a per-day child seat on a ten-day hire is ten times the number you typed.