To begin processing sales in Retail POS, you need to select a shop and a register. Once you do, the shop and register you selected display in main menu and the top bar of the Sale screen. This is to make sure you process sales in the correct shop and register throughout the course of your business day.
If for any reason you need to switch registers:
From the main menu, tap Manage Registers.
If you have multiple shops, tap your shop.
Tap the register you want to switch to.