With POS, staff will sell according to the Warehouse assigned on the Inventory module or sell to all warehouses.
Sell to all warehouses:
On the POS channel, so that staff can sell to all warehouses -> go to Settings menu under the Omni Sales module -> Default setting -> uncheck "On POS, staff will sell according to the Warehouse assigned on the Inventory module" -> Save.
Sell according to the Warehouse assigned on the Inventory module
Scenario: You have many stores and each store has a small amount of inventory. Each employee sells in one store. At this point, we need to create multiple warehouses, each representing a store. Then we import inventory for each store or transfer goods from the main warehouse to the store's warehouse. Then, assign the store's warehouse to the employee. At this time, on the POS channel, employees will only sell goods to the assigned warehouse.If a salesperson sells to multiple stores, assign the warehouses of those stores to them.
Steps to perform:
Step 1. Go to Settings menu under the Omni Sales module -> Default setting -> check "On POS, staff will sell according to the Warehouse assigned on the Inventory module" -> Save.
Step 2. Go to Warehouse menu under the Inventory module -> Create warehouse of store and assign it to your staff 
On the warehouse management screen, you can filter the assigned warehouse by employee.
Step 3. Import goods to store warehouses
Step 4. Go to POS channel and add product
Step 5. Go to POS store -> select the warehouse you want to get products to sell -> search and add products to cart -> select customer -> adjust quantity and click Payment
Step 6. In this step, if you choose both options: Create invoice and Inventory delivery voucher -> the product will be deducted from the warehouse you selected in the step above. If in this step you do not select Inventory delivery voucher, it means you will manually create inventory delivery voucher or go to order detail and press the Create export stock button, then the product will be exported according to the FIFO method.