diff --git a/ocpp1.6/core/authorize.go b/ocpp1.6/core/authorize.go
index 3a9874ad..ab48cf09 100644
--- a/ocpp1.6/core/authorize.go
+++ b/ocpp1.6/core/authorize.go
@@ -1,8 +1,9 @@
 package core
 
 import (
-	"github.com/lorenzodonini/ocpp-go/ocpp1.6/types"
 	"reflect"
+
+	"github.com/lorenzodonini/ocpp-go/ocpp1.6/types"
 )
 
 // -------------------- Authorize (CP -> CS) --------------------
@@ -11,7 +12,7 @@ const AuthorizeFeatureName = "Authorize"
 
 // The field definition of the Authorize request payload sent by the Charge Point to the Central System.
 type AuthorizeRequest struct {
-	IdTag string `json:"idTag" validate:"required,max=20"`
+	IdTag string `json:"idTag" validate:"omitempty,max=20"`
 }
 
 // This field definition of the Authorize confirmation payload, sent by the Charge Point to the Central System in response to an AuthorizeRequest.
diff --git a/ocpp1.6/core/start_transaction.go b/ocpp1.6/core/start_transaction.go
index 3b3bdaf6..3a0fef3d 100644
--- a/ocpp1.6/core/start_transaction.go
+++ b/ocpp1.6/core/start_transaction.go
@@ -1,8 +1,9 @@
 package core
 
 import (
-	"github.com/lorenzodonini/ocpp-go/ocpp1.6/types"
 	"reflect"
+
+	"github.com/lorenzodonini/ocpp-go/ocpp1.6/types"
 )
 
 // -------------------- Start Transaction (CP -> CS) --------------------
@@ -12,7 +13,7 @@ const StartTransactionFeatureName = "StartTransaction"
 // This field definition of the StartTransactionRequest payload sent by the Charge Point to the Central System.
 type StartTransactionRequest struct {
 	ConnectorId   int             `json:"connectorId" validate:"gt=0"`
-	IdTag         string          `json:"idTag" validate:"required,max=20"`
+	IdTag         string          `json:"idTag" validate:"omitempty,max=20"`
 	MeterStart    int             `json:"meterStart" validate:"gte=0"`
 	ReservationId *int            `json:"reservationId,omitempty" validate:"omitempty"`
 	Timestamp     *types.DateTime `json:"timestamp" validate:"required"`