1. In the administration panel, go to Add-ons > Manage add-ons and enable the 'Reward points' add-on.
2. In the administration panel, go to Products > Products.
3. Click on the link of the desired product.
4. Open the Reward points tab.
5. Select the Allow payment by points check box.
6. Select the Override global PER check box.
7. Enter the desired value in the Price in points input field.
8. Click the Save and close button.