If you want to give a discount to one specific customer, you can do that directly when selling the product.
Follow these steps:
First select the product that you wish to sell. Here we show how to sell a product.
Then, click on the green pencil symbol.
A pop-up appears where you can edit all the settings of this product:
You can give a discount (i.e. 50% or -50 EUR), or enter manually a new amount.
You can adapt the validity of the product or the number of credits it offers (i.e. in case the customer has used already some of them in your old system).
At the end, you always have to enter a reason.
Click on Save.
After modifying all the necessary settings, continue the sale by choosing the payment method.
Read here more info about how to sell a product.
In the invoice overview, you will see a a yellow discount symbol meaning that a discount was given for this product.