diff --git a/api/handlers.go b/api/handlers.go
index 4acbcf0..933079e 100644
--- a/api/handlers.go
+++ b/api/handlers.go
@@ -7,7 +7,9 @@ import (
 
 	"github.com/gin-gonic/gin"
 	"github.com/hermeznetwork/hermez-node/db/historydb"
+	"github.com/hermeznetwork/hermez-node/log"
 	"github.com/hermeznetwork/tracerr"
+	"github.com/lib/pq"
 )
 
 const (
@@ -25,6 +27,9 @@ const (
 
 	// 2^64 /2 -1
 	maxInt64 = 9223372036854775807
+
+	// Error for duplicated key
+	errDuplicatedKey = "Item already exists"
 )
 
 var (
@@ -33,6 +38,15 @@ var (
 )
 
 func retSQLErr(err error, c *gin.Context) {
+	log.Warn("HTTP API SQL request error", "err", err)
+	if sqlErr, ok := tracerr.Unwrap(err).(*pq.Error); ok {
+		// https://www.postgresql.org/docs/current/errcodes-appendix.html
+		if sqlErr.Code == "23505" {
+			c.JSON(http.StatusInternalServerError, errorMsg{
+				Message: errDuplicatedKey,
+			})
+		}
+	}
 	if tracerr.Unwrap(err) == sql.ErrNoRows {
 		c.JSON(http.StatusNotFound, errorMsg{
 			Message: err.Error(),
@@ -45,6 +59,7 @@ func retSQLErr(err error, c *gin.Context) {
 }
 
 func retBadReq(err error, c *gin.Context) {
+	log.Warn("HTTP API Bad request error", "err", err)
 	c.JSON(http.StatusBadRequest, errorMsg{
 		Message: err.Error(),
 	})
diff --git a/api/swagger.yml b/api/swagger.yml
index bdd7e18..a462aee 100644
--- a/api/swagger.yml
+++ b/api/swagger.yml
@@ -2193,6 +2193,11 @@ components:
           description: Recommended fee if the destination account of the transaction doesn't exist, but the coordinator has the ability to create a valid account associated to a BJJ public key controlled by the receiver. Note that these kind of accounts are not associated with an Ethereum address and therefore can only operate in L2. 
           minimum: 0
           example: 0.5
+      required:
+        - existingAccount
+        - createAccount
+        - createAccountInternal
+      additionalProperties: false
     Token:
       type: object
       description: Hermez Network compatible and registered token.
diff --git a/common/fee.go b/common/fee.go
index 9b28f08..14c1449 100644
--- a/common/fee.go
+++ b/common/fee.go
@@ -22,9 +22,9 @@ var FeeFactorLsh60 [256]*big.Int
 // the coordinator according to the tx type (if the tx requires to create an
 // account and register, only register or he account already esists)
 type RecommendedFee struct {
-	ExistingAccount           float64
-	CreatesAccount            float64
-	CreatesAccountAndRegister float64
+	ExistingAccount           float64 `json:"existingAccount"`
+	CreatesAccount            float64 `json:"createAccount"`
+	CreatesAccountAndRegister float64 `json:"createAccountInternal"`
 }
 
 // FeeSelector is used to select a percentage from the FeePlan.