diff --git a/backend/app/http/posts.go b/backend/app/http/posts.go
index 8fa0264..13bf360 100644
--- a/backend/app/http/posts.go
+++ b/backend/app/http/posts.go
@@ -269,7 +269,8 @@ func (ctl *posts) Buy(ctx fiber.Ctx, id int64, user *model.Users) (*wechat.JSAPI
 			Expire(30 * time.Minute).
 			Description(post.Title).
 			OutTradeNo(order.OrderNo).
-			Payer(user.OpenID)
+			Payer(user.OpenID).
+			CNYAmount(post.Price * int64(post.Discount) / 100)
 	})
 	if err != nil {
 		log.Errorf("wepay.V3TransactionJsapi err: %v", err)
diff --git a/backend/providers/wepay/pay.go b/backend/providers/wepay/pay.go
index 115833a..bf63a7e 100644
--- a/backend/providers/wepay/pay.go
+++ b/backend/providers/wepay/pay.go
@@ -185,12 +185,18 @@ func (b *BodyMap) OutTradeNo(outTradeNo string) *BodyMap {
 }
 
 // Amount
-func (b *BodyMap) Amount(total int, currency string) *BodyMap {
+func (b *BodyMap) Amount(total int64, currency CURRENCY) *BodyMap {
 	return b.SetBodyMap("amount", func(bm gopay.BodyMap) {
-		bm.Set("total", total).Set("currency", currency)
+		bm.
+			Set("total", total).
+			Set("currency", currency.String())
 	})
 }
 
+func (b *BodyMap) CNYAmount(total int64) *BodyMap {
+	return b.Amount(total, CNY)
+}
+
 // Payer
 func (b *BodyMap) Payer(spOpenId string) *BodyMap {
 	return b.SetBodyMap("payer", func(bm gopay.BodyMap) {
@@ -202,3 +208,15 @@ func (b *BodyMap) Payer(spOpenId string) *BodyMap {
 func (b *BodyMap) SubMchId(subMchId string) *BodyMap {
 	return b.Set("sub_mchid", subMchId)
 }
+
+type CURRENCY string
+
+func (c CURRENCY) String() string {
+	return string(c)
+}
+
+const (
+	CNY CURRENCY = "CNY"
+	USD CURRENCY = "USD"
+	EUR CURRENCY = "EUR"
+)