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 > scroll and click to Marketing > click on Promotions.
You will find the page as shown below.
Click on Add Coupon.
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!