Similar to Barcode Scanning in Sales Orders and Stock Transfer, you can scan to add products into the Purchase Order, simple as that.
There are two ways to scan products in Purchase Order:
Click on the Scan button on Purchase Order listing page to create a new Sales Order and scan
Create new Purchase Order and click Barcode Scanning on the bottom left to start scanning products.
A modal will pop up, you can start scanning and once done, click Add Item to add the products into the Purchase Order. The product number will change if the barcodes match.
