Setting the amount of discount does not do anything by itself.
Under "Settings" you have 2 options to consider to flag on.
"Participate in Sale offs" - applies your chosen amount of discount during sitewide sales
(green badge at the upper left corner with the pecentage applied).
"Participate in CGTrader Loyalty Discounts" - allows customers to use their "Loyalty Credits" for purchase (red piggy bank icon at the upper left corner).
As there is no ongoing sitewide sales at this moment, you have to check the
"Participate in CGTrader Loyalty Discounts" option to offer discount.
...and don't forget to scroll down and click on the green "Update information" button to save and apply the changes you've just made...