1. In the administration panel, go to Add-ons > Manage add-ons.
2. Click on the name of the Reward points add-on.
3. Enter the desired number of reward points in the Points Exchange Rate (PER - the number of points equal to 1 conventional unit) input field.
4. Click the Save button.
5. In the administration panel, go to Products > Products.
6. Click on the link of the desired product.
7. Open the Reward points tab.
8. Select the Allow payment by points check box.
9. Click the Save and close button.
   

   
   
   

NOTE: In order to enable the Allow payment by points option for all the products at once you should use the Edit selected functionality. Please refer to this article.

Make sure that the Override global PER option is disabled for  products for which you would like to set up a price in points according  to a ratio on their details page.