diff --git a/api/accountcreationauths.go b/api/accountcreationauths.go
index f5a562d..46e55a8 100644
--- a/api/accountcreationauths.go
+++ b/api/accountcreationauths.go
@@ -21,7 +21,7 @@ func (a *API) postAccountCreationAuth(c *gin.Context) {
 	}
 	// API to common + verify signature
 	commonAuth := accountCreationAuthAPIToCommon(&apiAuth)
-	if !commonAuth.VerifySignature(a.chainID, a.hermezAddress) {
+	if !commonAuth.VerifySignature(a.cg.ChainID, a.hermezAddress) {
 		retBadReq(errors.New("invalid signature"), c)
 		return
 	}
diff --git a/api/api.go b/api/api.go
index d8e2c20..8295d35 100644
--- a/api/api.go
+++ b/api/api.go
@@ -40,7 +40,6 @@ type API struct {
 	h             *historydb.HistoryDB
 	cg            *configAPI
 	l2            *l2db.L2DB
-	chainID       uint16
 	hermezAddress ethCommon.Address
 }
 
@@ -68,9 +67,9 @@ func NewAPI(
 			RollupConstants:   *newRollupConstants(consts.Rollup),
 			AuctionConstants:  consts.Auction,
 			WDelayerConstants: consts.WDelayer,
+			ChainID:           consts.ChainID,
 		},
 		l2:            l2db,
-		chainID:       consts.ChainID,
 		hermezAddress: consts.HermezAddress,
 	}
 
diff --git a/api/api_test.go b/api/api_test.go
index 25046fc..e497d60 100644
--- a/api/api_test.go
+++ b/api/api_test.go
@@ -215,6 +215,7 @@ func TestMain(m *testing.M) {
 	chainID := uint16(0)
 	_config := getConfigTest(chainID)
 	config = configAPI{
+		ChainID:           chainID,
 		RollupConstants:   *newRollupConstants(_config.RollupConstants),
 		AuctionConstants:  _config.AuctionConstants,
 		WDelayerConstants: _config.WDelayerConstants,
diff --git a/api/config.go b/api/config.go
index 93292c9..7efd056 100644
--- a/api/config.go
+++ b/api/config.go
@@ -57,6 +57,7 @@ type Config struct {
 }
 
 type configAPI struct {
+	ChainID           uint16                   `json:"chainId"`
 	RollupConstants   rollupConstants          `json:"hermez"`
 	AuctionConstants  common.AuctionConstants  `json:"auction"`
 	WDelayerConstants common.WDelayerConstants `json:"withdrawalDelayer"`
diff --git a/api/swagger.yml b/api/swagger.yml
index a1e70e8..04e430b 100644
--- a/api/swagger.yml
+++ b/api/swagger.yml
@@ -3040,10 +3040,15 @@ components:
             - maxEmergencyModeTime
             - hermezRollup
           additionalProperties: false
+        chainId:
+          type: integer
+          description: Id of the chain
+          example: 27
       required:
         - hermez
         - auction
         - withdrawalDelayer
+        - chainId
       additionalProperties: false
     Error:
       type: object
diff --git a/api/txspool.go b/api/txspool.go
index 11cd878..06d5224 100644
--- a/api/txspool.go
+++ b/api/txspool.go
@@ -187,7 +187,7 @@ func (a *API) verifyPoolL2TxWrite(txw *l2db.PoolL2TxWrite) error {
 			poolTx.TokenID, account.TokenID))
 	}
 	// Check signature
-	if !poolTx.VerifySignature(a.chainID, account.BJJ) {
+	if !poolTx.VerifySignature(a.cg.ChainID, account.BJJ) {
 		return tracerr.Wrap(errors.New("wrong signature"))
 	}
 	return nil