fix(coupon): add expiration check and error handling for expired coupons

pkg/xerr/errCode.go

@@ -57,6 +57,7 @@ const (
 	CouponAlreadyUsed       uint32 = 50002 // Coupon has already been used
 	CouponNotApplicable     uint32 = 50003 // Coupon does not match the order or conditions
 	CouponInsufficientUsage uint32 = 50004 // Coupon has insufficient remaining uses
+	CouponExpired           uint32 = 50005 // Coupon is expired
 )
 
 // Subscribe

pkg/xerr/errMsg.go

@@ -46,6 +46,7 @@ func init() {
 		CouponAlreadyUsed:       "Coupon has already been used",
 		CouponNotApplicable:     "Coupon does not match the order or conditions",
 		CouponInsufficientUsage: "Coupon has insufficient remaining uses",
+		CouponExpired:           "Coupon is expired",
 
 		// Subscribe
 		SubscribeExpired:                "Subscribe is expired",