On checking the box for “Use customer price categories”, mSupply will activate the price categories.

By default all customers are assigned a price category of “A”

To assign a different category to a customer, choose Customers > Show customers… and find the customer entry. Then set the price category field to a different value

Here in the Preferences, you specify what percentage change to the default price will be made for each category.

For example, you might have a group of customers to whom you charge commercial prices, which are 20% above your normal price. Enter “20” in the “B” category field, then assign your private customers a price category of “B”