diff --git a/Makefile b/Makefile
index b0d07d0..c3a8d11 100644
--- a/Makefile
+++ b/Makefile
@@ -34,7 +34,7 @@ test:
 ## Run integration tests
 .PHONY: integration-test
 integration-test:
-	go test -tags integration -run="$(testcase)" ./...
+	go test -tags integration -run="$(testcase)" -cover ./...
 
 ## Run lint
 .PHONY: lint
diff --git a/README.md b/README.md
index c0cae2f..30e992c 100644
--- a/README.md
+++ b/README.md
@@ -39,7 +39,7 @@ The testcase variable could be used to run a specific test
 
 ## Ship a new version
     `make image/publish`
-    `heroky container:release web -a contractus`
+    `heroku container:release web -a contractus`
 
 ## Logs in production
     `heroku logs --tail -a contractus`
diff --git a/api/api.go b/api/api.go
index 844b2d0..10760bb 100644
--- a/api/api.go
+++ b/api/api.go
@@ -3,6 +3,7 @@ package api
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -23,13 +24,20 @@ type Error struct {
 func (e Error) Error() string {
 	return fmt.Sprintf("%s: %s", e.Code, e.Msg)
 }
+
 func sendErr(w http.ResponseWriter, statusCode int, err error) {
+	var httpErr Error
+	if !errors.As(err, &httpErr) {
+		httpErr = Error{
+			Code: "unknown_error",
+			Msg:  "An unexpected error happened",
+		}
+	}
 	if statusCode >= 500 {
-		slog.Error("Internal server error", "error", err)
+		slog.Error("Unable to process request", "error", err.Error(), "status_code", statusCode)
 	}
-	err = Error{Code: "internal_server_error error", Msg: "Internal server error"}
 
-	send(w, statusCode, err)
+	send(w, statusCode, httpErr)
 }
 
 func send(w http.ResponseWriter, statusCode int, body interface{}) {
@@ -64,6 +72,7 @@ func parseFile(r *http.Request) (content string, err error) {
 	return string(contentByte), nil
 }
 
+// convert is an internal function responsible for converting the file content into transactions.
 func convert(content string) (t []contractus.Transaction, err error) {
 	content = strings.Replace(content, "\t", "", -1)
 	var re = regexp.MustCompile(`(?m).*$\n`)
diff --git a/api/api_test.go b/api/api_test.go
index 8bd2118..fd3ad7d 100644
--- a/api/api_test.go
+++ b/api/api_test.go
@@ -4,6 +4,9 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
+	"time"
+
+	"github.com/perebaj/contractus"
 )
 
 // TODO(JOJO) assert the body
@@ -26,3 +29,62 @@ func TestSend(t *testing.T) {
 		t.Errorf("expected status code %d, got %d", http.StatusOK, w.Code)
 	}
 }
+
+func TestConvert(t *testing.T) {
+	content := `12022-01-15T19:20:30-03:00CURSO DE BEM-ESTAR            0000012750JOSE CARLOS
+	12021-12-03T11:46:02-03:00DOMINANDO INVESTIMENTOS       0000050000MARIA CANDIDA
+	`
+	transac, err := convert(content)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	want := []contractus.Transaction{
+		{
+			Type:               1,
+			Date:               time.Date(2022, 01, 15, 22, 20, 30, 0, time.UTC),
+			ProductDescription: "CURSO DE BEM-ESTAR",
+			ProductPriceCents:  12750,
+			SellerName:         "JOSE CARLOS",
+			SellerType:         "producer",
+			Action:             "venda produtor",
+		},
+		{
+			Type:               1,
+			Date:               time.Date(2021, 12, 03, 14, 46, 02, 0, time.UTC),
+			ProductDescription: "DOMINANDO INVESTIMENTOS",
+			ProductPriceCents:  50000,
+			SellerName:         "MARIA CANDIDA",
+			SellerType:         "producer",
+			Action:             "venda produtor",
+		},
+	}
+
+	if len(transac) == len(want) {
+		assert(t, transac[0].Type, want[0].Type)
+		assert(t, transac[0].Date.Format(time.RFC3339), want[0].Date.Format(time.RFC3339))
+		assert(t, transac[0].ProductDescription, want[0].ProductDescription)
+		assert(t, transac[0].ProductPriceCents, want[0].ProductPriceCents)
+		assert(t, transac[0].SellerName, want[0].SellerName)
+		assert(t, transac[0].SellerType, want[0].SellerType)
+		assert(t, transac[0].Action, want[0].Action)
+
+		assert(t, transac[1].Type, want[1].Type)
+		assert(t, transac[1].Date.Format(time.RFC3339), want[1].Date.Format(time.RFC3339))
+		assert(t, transac[1].ProductDescription, want[1].ProductDescription)
+		assert(t, transac[1].ProductPriceCents, want[1].ProductPriceCents)
+		assert(t, transac[1].SellerName, want[1].SellerName)
+		assert(t, transac[1].SellerType, want[1].SellerType)
+		assert(t, transac[1].Action, want[1].Action)
+	} else {
+		t.Fatalf("expected %d transactions, got %d", len(want), len(transac))
+	}
+}
+
+func assert(t *testing.T, got, want interface{}) {
+	t.Helper()
+
+	if got != want {
+		t.Fatalf("got %v want %v", got, want)
+	}
+}
diff --git a/api/transactionhandler.go b/api/transactionhandler.go
index d0311b9..5f5195a 100644
--- a/api/transactionhandler.go
+++ b/api/transactionhandler.go
@@ -12,10 +12,12 @@ import (
 
 	"github.com/go-chi/chi/v5"
 	"github.com/perebaj/contractus"
+	"github.com/perebaj/contractus/postgres"
 )
 
 type transactionStorage interface {
 	SaveTransaction(ctx context.Context, t []contractus.Transaction) error
+	Balance(ctx context.Context, sellerType, sellerName string) (*contractus.BalanceResponse, error)
 }
 
 type transactionHandler struct {
@@ -29,18 +31,55 @@ func RegisterHandler(r chi.Router, storage transactionStorage) {
 	}
 
 	const balanceProducer = "/balance/producer"
-	r.Method(http.MethodGet, balanceProducer, http.HandlerFunc(h.balance))
+	r.Method(http.MethodGet, balanceProducer, http.HandlerFunc(h.producerBalance))
+
+	const balanceAffiliate = "/balance/affiliate"
+	r.Method(http.MethodGet, balanceAffiliate, http.HandlerFunc(h.affiliateBalance))
 
 	const upload = "/upload"
 	r.Method(http.MethodPost, upload, http.HandlerFunc(h.upload))
 }
 
-func (s transactionHandler) balance(w http.ResponseWriter, _ *http.Request) {
-	t := struct {
-		ProducerID string `json:"producer_id"`
-	}{ProducerID: "123"}
+func (s transactionHandler) producerBalance(w http.ResponseWriter, r *http.Request) {
+	query := r.URL.Query()
+	name := query.Get("name")
+	if name == "" {
+		sendErr(w, http.StatusBadRequest, fmt.Errorf("name is required"))
+		return
+	}
+
+	b, err := s.storage.Balance(r.Context(), "producer", name)
+	if err != nil {
+		if err == postgres.ErrSellerNotFound {
+			sendErr(w, http.StatusNotFound, postgres.ErrSellerNotFound)
+			return
+		}
+		sendErr(w, http.StatusInternalServerError, err)
+		return
+	}
+
+	send(w, http.StatusOK, b)
+}
+
+func (s transactionHandler) affiliateBalance(w http.ResponseWriter, r *http.Request) {
+	query := r.URL.Query()
+	name := query.Get("name")
+	if name == "" {
+		sendErr(w, http.StatusBadRequest, fmt.Errorf("name is required"))
+		return
+	}
+
+	b, err := s.storage.Balance(r.Context(), "affiliate", name)
+	if err != nil {
+		if err == postgres.ErrSellerNotFound {
+			sendErr(w, http.StatusNotFound, postgres.ErrSellerNotFound)
+			return
+		}
+		sendErr(w, http.StatusInternalServerError, err)
+		return
+	}
 
-	send(w, http.StatusOK, t)
+	send(w, http.StatusOK, b)
 }
 
 func (s transactionHandler) upload(w http.ResponseWriter, r *http.Request) {
diff --git a/api/transactionhandler_test.go b/api/transactionhandler_test.go
index 169cf11..8f755b2 100644
--- a/api/transactionhandler_test.go
+++ b/api/transactionhandler_test.go
@@ -8,7 +8,6 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"testing"
-	"time"
 
 	"github.com/go-chi/chi/v5"
 	"github.com/perebaj/contractus"
@@ -20,6 +19,10 @@ func (m *mockTransactionStorage) SaveTransaction(_ context.Context, _ []contract
 	return nil
 }
 
+func (m *mockTransactionStorage) Balance(_ context.Context, _ string, _ string) (*contractus.BalanceResponse, error) {
+	return nil, nil
+}
+
 func TestTransactionHandlerUpload(t *testing.T) {
 	var b bytes.Buffer
 	w := multipart.NewWriter(&b)
@@ -54,61 +57,32 @@ func TestTransactionHandlerUpload(t *testing.T) {
 	}
 }
 
-func TestConvert(t *testing.T) {
-	content := `12022-01-15T19:20:30-03:00CURSO DE BEM-ESTAR            0000012750JOSE CARLOS
-	12021-12-03T11:46:02-03:00DOMINANDO INVESTIMENTOS       0000050000MARIA CANDIDA
-	`
-	transac, err := convert(content)
-	if err != nil {
-		t.Fatal(err)
-	}
+func TestTransactionHandlerBalanceProducer(t *testing.T) {
+	m := &mockTransactionStorage{}
+	r := chi.NewRouter()
+	RegisterHandler(r, m)
 
-	want := []contractus.Transaction{
-		{
-			Type:               1,
-			Date:               time.Date(2022, 01, 15, 22, 20, 30, 0, time.UTC),
-			ProductDescription: "CURSO DE BEM-ESTAR",
-			ProductPriceCents:  12750,
-			SellerName:         "JOSE CARLOS",
-			SellerType:         "producer",
-			Action:             "venda produtor",
-		},
-		{
-			Type:               1,
-			Date:               time.Date(2021, 12, 03, 14, 46, 02, 0, time.UTC),
-			ProductDescription: "DOMINANDO INVESTIMENTOS",
-			ProductPriceCents:  50000,
-			SellerName:         "MARIA CANDIDA",
-			SellerType:         "producer",
-			Action:             "venda produtor",
-		},
-	}
+	req := httptest.NewRequest(http.MethodGet, "/balance/producer?name=JOSE", nil)
+	resp := httptest.NewRecorder()
+
+	r.ServeHTTP(resp, req)
 
-	if len(transac) == len(want) {
-		assert(t, transac[0].Type, want[0].Type)
-		assert(t, transac[0].Date.Format(time.RFC3339), want[0].Date.Format(time.RFC3339))
-		assert(t, transac[0].ProductDescription, want[0].ProductDescription)
-		assert(t, transac[0].ProductPriceCents, want[0].ProductPriceCents)
-		assert(t, transac[0].SellerName, want[0].SellerName)
-		assert(t, transac[0].SellerType, want[0].SellerType)
-		assert(t, transac[0].Action, want[0].Action)
-
-		assert(t, transac[1].Type, want[1].Type)
-		assert(t, transac[1].Date.Format(time.RFC3339), want[1].Date.Format(time.RFC3339))
-		assert(t, transac[1].ProductDescription, want[1].ProductDescription)
-		assert(t, transac[1].ProductPriceCents, want[1].ProductPriceCents)
-		assert(t, transac[1].SellerName, want[1].SellerName)
-		assert(t, transac[1].SellerType, want[1].SellerType)
-		assert(t, transac[1].Action, want[1].Action)
-	} else {
-		t.Fatalf("expected %d transactions, got %d", len(want), len(transac))
+	if resp.Code != http.StatusOK {
+		t.Fatalf("expected status code %d, got %d", http.StatusOK, resp.Code)
 	}
 }
 
-func assert(t *testing.T, got, want interface{}) {
-	t.Helper()
+func TestTransactionHandlerBalanceAffiliate(t *testing.T) {
+	m := &mockTransactionStorage{}
+	r := chi.NewRouter()
+	RegisterHandler(r, m)
 
-	if got != want {
-		t.Fatalf("got %v want %v", got, want)
+	req := httptest.NewRequest(http.MethodGet, "/balance/affiliate?name=JOSE", nil)
+	resp := httptest.NewRecorder()
+
+	r.ServeHTTP(resp, req)
+
+	if resp.Code != http.StatusOK {
+		t.Fatalf("expected status code %d, got %d", http.StatusOK, resp.Code)
 	}
 }
diff --git a/docs/api.md b/docs/api.md
index b2d2a43..5c17473 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -8,10 +8,48 @@ Basic usage examples of the contractus API
 
 Request:
 
-```
+```bash
     curl -i -X 'POST' \
         'http://localhost:8080/upload' \
         -H 'accept: application/json' \
         -H 'Content-Type: multipart/form-data' \
         -F 'file=@sales.txt;type=text/plain'
 ```
+
+## `/balance/affiliate?name=<>`
+
+Request: 
+
+```bash
+curl -X 'GET' \
+  'http://localhost:8080/balance/affiliate?name=<>' \
+  -H 'accept: application/json'
+```
+
+Response:
+
+```JSON
+{
+  "balance": 0,
+  "seller_name": "string"
+}
+```
+
+## `/balance/producer?name=<>`
+
+Request: 
+
+```bash
+curl -X 'GET' \
+  'http://localhost:8080/balance/producer?name=<>' \
+  -H 'accept: application/json'
+```
+
+Response:
+
+```JSON
+{
+  "balance": 0,
+  "seller_name": "string"
+}
+```
diff --git a/docs/api.yml b/docs/api.yml
index d97d11e..2de8d92 100644
--- a/docs/api.yml
+++ b/docs/api.yml
@@ -6,16 +6,6 @@ info:
 servers:
   - url: http://localhost:8080
 paths:
-  /health:
-    get:
-      responses:
-        '200':
-          description: OK
-          content:
-            application/json:
-              schema:
-                type: string
-                default: 'Jojo is awesome!'
   /upload:
     post:
       summary: Upload a transaction file
@@ -79,6 +69,12 @@ paths:
                   seller_name:
                     type: string
                     description: Affiliate name
+        '404':
+          description: Not found
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ErrorResponse'
           
   /balance/producer:
     get:
@@ -106,6 +102,12 @@ paths:
                   seller_name:
                     type: string
                     description: Producer name
+        '404':
+          description: Not found
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/ErrorResponse'
 components:
   schemas:
     ErrorResponse:
@@ -114,7 +116,7 @@ components:
         code:
           type: string
           description: Error code error
-        message:
+        msg:
           type: string
           description: Error message
     Transaction:
diff --git a/postgres/storage.go b/postgres/storage.go
index f9e7426..df11735 100644
--- a/postgres/storage.go
+++ b/postgres/storage.go
@@ -2,11 +2,17 @@ package postgres
 
 import (
 	"context"
+	"errors"
 
 	"github.com/jmoiron/sqlx"
 	"github.com/perebaj/contractus"
 )
 
+var (
+	// ErrSellerNotFound is returned when the seller is not found in the database.
+	ErrSellerNotFound = errors.New("seller not found")
+)
+
 // Storage deal with the database layer for transactions.
 type Storage struct {
 	db *sqlx.DB
@@ -58,6 +64,9 @@ func (s Storage) Balance(ctx context.Context, sellerType, sellerName string) (*c
 		WHERE seller_type = $1 AND seller_name = $2
 	`, sellerType, sellerName)
 
+	if len(transactions) == 0 {
+		return nil, ErrSellerNotFound
+	}
 	if err != nil {
 		return nil, err
 	}
diff --git a/postgres/storage_test.go b/postgres/storage_test.go
index 6c3c346..a557e7b 100644
--- a/postgres/storage_test.go
+++ b/postgres/storage_test.go
@@ -5,6 +5,7 @@ package postgres_test
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"net/url"
 	"os"
@@ -253,6 +254,36 @@ func TestStorageBalance(t *testing.T) {
 	assert(t, got.SellerName, "CARLOS BATISTA")
 }
 
+func TestStorageBalance_NotFound(t *testing.T) {
+	db := OpenDB(t)
+	storage := postgres.NewStorage(db)
+	ctx := context.Background()
+
+	transactions1 := []contractus.Transaction{
+		{
+			Type:               1,
+			Date:               time.Now().UTC(),
+			ProductDescription: "Product description",
+			ProductPriceCents:  12750,
+			SellerName:         "JOSE CARLOS",
+			SellerType:         "producer",
+			Action:             "venda produtor",
+		},
+	}
+
+	err := storage.SaveTransaction(ctx, transactions1)
+	if err != nil {
+		t.Fatalf("error saving transactions 1: %v", err)
+	}
+
+	got, err := storage.Balance(ctx, "producer", "INVALID NAME")
+	if !errors.Is(err, postgres.ErrSellerNotFound) {
+		t.Fatalf("error getting balance: %v", err)
+	}
+
+	assert(t, got, (*contractus.BalanceResponse)(nil))
+}
+
 func assert(t *testing.T, got, want interface{}) {
 	t.Helper()