When you run a campaign or a sale, you can provide your coupon code so that customers will be eager to buy more. But, you also need to limit the usage of the coupon code to avoid any loss. Here's how you can do it:
Go to your Dashboard > click Configuration > click on Promotion.
Click on the orange icon to edit any of the coupon codes that you have.
Here, you can see the button that is used to limit the coupon code.
Key in your desired number and don't forget to click Submit to save the changes that you have made!