reset service fee

@@ -183,14 +183,21 @@ public class SellerOrderComputeService {
      */
     private Optional<CouponPayResult> activityCouponUse(UserCouponsBo activityCouponsBo, SellerOrderRelatedBuyerOrderContext chargeContext) {
         SellerOrderComputeResult chargeResult = chargeContext.getSellerOrderComputeResult();
+
         PlatformFeeDto platformFeeDto = chargeResult.getPlatformFee();
-        BigDecimal couponPayAmount = BigDecimalHelper.min(platformFeeDto.getServiceFee(), activityCouponsBo.getCouponAmount());
+
+        BigDecimal oldServiceFee = platformFeeDto.getServiceFee();
+        //1. calculate coupon cut amount
+        BigDecimal couponPayAmount = BigDecimalHelper.min(oldServiceFee, activityCouponsBo.getCouponAmount());
         BigDecimal oldIncome = chargeResult.getIncome();
+        //2. calculate income and set
+        //2.1
         BigDecimal newIncome = BigDecimalHelper.add(oldIncome, couponPayAmount);
-        //set income
+        //2.2 set income
         chargeResult.setIncome(newIncome);
-
-        //
+        //3. calculate serviceFee and set
+        BigDecimal newServiceFee = BigDecimalHelper.sub(oldServiceFee, couponPayAmount);
+        platformFeeDto.setServiceFee(newServiceFee);
 
         BigDecimal oldFinalAmountOfCutCoupons = chargeResult.getCouponCutAmount();
         BigDecimal newFinalAmountOfCutCoupons;