The customer reports
"The issue is when there is two people trying to book the same slot at once. If the first user and the second user have the slots page open at the same time, they can both book the same slot. Rather than one use confirms/books the slot and the second user gets a denied message."
Conclusion
Essentially, we check the availability on the [user]/[type] page, but once you actually get to the booking details page, it doesn't check if the slot is available again before making the booking. This means that if two people are on the /book page, you can double-book a slot.
The customer reports
"The issue is when there is two people trying to book the same slot at once. If the first user and the second user have the slots page open at the same time, they can both book the same slot. Rather than one use confirms/books the slot and the second user gets a denied message."
Conclusion
Essentially, we check the availability on the [user]/[type] page, but once you actually get to the booking details page, it doesn't check if the slot is available again before making the booking. This means that if two people are on the /book page, you can double-book a slot.