Not enough kit to go round
You sell twelve canyoning places, then find out in the morning there are only ten wetsuits in the right sizes, or the big minibus is already out on another trip. Your real capacity is set by your kit, not your website.
Add wetsuits, helmets, kayaks and minibuses as resources with their capacity, assign them to each session or group, and see at a glance what is still free.
