Customer browsing products and adds items to cart Proceeds to checkout view In checkout form, sees "Have a coupon?" section Enters coupon code into field Clicks "Apply" button AJAX request validates coupon code with Portal server If valid: Discount calculated and displayed, "Apply" button hidden, "Remove" button shown If invalid: Error message displayed in red, coupon field remains enabled for retry Continues with order with discount applied Upon payment: Coupon usage incremented on server, usage count updated Percentage Discount: Order subtotal × (value / 100) = discount amount Fixed Amount Discount: Fixed value in currency (e.g., $10) Applied To: Subtotal before tax Taxes: Calculated on subtotal minus discount Display: Shows "Discount (CODE - X% off)" or "Discount (CODE - $X off)" in