diff --git a/api/README.md b/api/README.md
index 8a77480f..a2e98bb1 100644
--- a/api/README.md
+++ b/api/README.md
@@ -77,6 +77,7 @@ Triggers a new scan for the provided token, starting from the defined block.
 | HTTP Status  | Message | Internal error |
 |:---:|:---|:---:|
 | 400 | `malformed token information` | 4000 | 
+| 409 | `token already created` | 4009 | 
 | 500 | `the token cannot be created` | 5000 | 
 | 500 | `error getting token information` | 5004 | 
 | 500 | `error initialising web3 client` | 5018 | 
@@ -114,6 +115,7 @@ Returns the information about the token referenced by the provided ID.
 | 404 | `no token found` | 4003 |
 | 500 | `error getting token information` | 5004 | 
 | 500 | `error initialising web3 client` | 5018 | 
+| 500 | `error getting last block number from web3 endpoint` | 5021 | 
 | 500 | `error encoding tokens` | 5011 | 
 
 **MVP Warn**: If `defaultStrategy` is `0`, no strategy (neither the dummy strategy) is associated to the given token.
diff --git a/api/censuses.go b/api/censuses.go
index e83dcecc..190b74d5 100644
--- a/api/censuses.go
+++ b/api/censuses.go
@@ -42,7 +42,7 @@ func (capi *census3API) getCensus(msg *api.APIdata, ctx *httprouter.HTTPContext)
 	// begin a transaction for group sql queries
 	tx, err := capi.db.BeginTx(internalCtx, nil)
 	if err != nil {
-		return err
+		return ErrCantGetCensus
 	}
 	defer func() {
 		if err := tx.Rollback(); err != nil {
@@ -97,7 +97,7 @@ func (capi *census3API) createAndPublishCensus(msg *api.APIdata, ctx *httprouter
 	// begin a transaction for group sql queries
 	tx, err := capi.db.BeginTx(internalCtx, nil)
 	if err != nil {
-		return err
+		return ErrCantCreateCensus
 	}
 	defer func() {
 		if err := tx.Rollback(); err != nil && !errors.Is(sql.ErrTxDone, err) {
diff --git a/api/errors.go b/api/errors.go
index 3d5a49d9..adbf0b5e 100644
--- a/api/errors.go
+++ b/api/errors.go
@@ -2,6 +2,7 @@ package api
 
 import (
 	"fmt"
+	"net/http"
 
 	"go.vocdoni.io/dvote/httprouter/apirest"
 )
@@ -52,6 +53,11 @@ var (
 		HTTPstatus: apirest.HTTPstatusNoContent,
 		Err:        fmt.Errorf("no strategy found"),
 	}
+	ErrTokenAlreadyExists = apirest.APIerror{
+		Code:       4009,
+		HTTPstatus: http.StatusConflict,
+		Err:        fmt.Errorf("token already created"),
+	}
 	ErrCantCreateToken = apirest.APIerror{
 		Code:       5000,
 		HTTPstatus: apirest.HTTPstatusInternalErr,
@@ -157,4 +163,9 @@ var (
 		HTTPstatus: apirest.HTTPstatusInternalErr,
 		Err:        fmt.Errorf("error counting census size"),
 	}
+	ErrCantGetLastBlockNumber = apirest.APIerror{
+		Code:       5021,
+		HTTPstatus: apirest.HTTPstatusInternalErr,
+		Err:        fmt.Errorf("error getting last block number from web3 endpoint"),
+	}
 )
diff --git a/api/tokens.go b/api/tokens.go
index 2fbab8d3..e44b1336 100644
--- a/api/tokens.go
+++ b/api/tokens.go
@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"errors"
 	"math/big"
+	"strings"
 	"time"
 
 	"github.com/ethereum/go-ethereum/common"
@@ -140,6 +141,9 @@ func (capi *census3API) createToken(msg *api.APIdata, ctx *httprouter.HTTPContex
 		Tag:           *tag,
 	})
 	if err != nil {
+		if strings.Contains(err.Error(), "UNIQUE constraint failed") {
+			return ErrTokenAlreadyExists
+		}
 		log.Errorw(err, "error creating token on the database")
 		return ErrCantCreateToken.Withf("error creating token with address %s", addr)
 	}
@@ -193,12 +197,12 @@ func (capi *census3API) getToken(msg *api.APIdata, ctx *httprouter.HTTPContext)
 		// get last block of the network, if something fails return progress 0
 		w3 := state.Web3{}
 		if err := w3.Init(internalCtx, capi.web3, address, state.TokenType(tokenData.TypeID)); err != nil {
-			return ErrInitializingWeb3
+			return ErrInitializingWeb3.WithErr(err)
 		}
 		// fetch the last block header and calculate progress
 		lastBlockNumber, err := w3.LatestBlockNumber(internalCtx)
 		if err != nil {
-			return ErrCantGetToken
+			return ErrCantGetLastBlockNumber
 		}
 		tokenProgress = uint64(float64(atBlock) / float64(lastBlockNumber) * 100)
 	}