How to receive a warning message if the selling price mentioned in the invoice is less than the purchase price on web?

To receive warning message, please follow the below mentioned steps:

Step 1 : Go to Settings.

Step 2 : Under General settings, Select Preferences.

Step 3 : And then under Document >> Click on Sales.

Step 4 : Enable the toggle of Warn user while creating invoice when price is less than purchase price of the item.

Step 5 : Scroll down and click on Save & Update.