FIFO means the oldest stock is sold first. In practice, this means: when you restock a shelf, the new bottles go behind the existing ones, not in front. Customers naturally pick from the front, so the oldest product moves first.
The challenge in vape retail is that products come in many small boxes with multiple flavours. The simplest implementation: label every box with the receipt date, and on each shelf place the oldest boxes on the left. Train staff to restock from the left side.
TrackElf removes the physical discipline requirement: it tracks every batch by date and colour-codes them, so even if staff restock randomly, the system flags which products need to go out first.