diff --git a/veza-backend-api/internal/core/marketplace/invoice_test.go b/veza-backend-api/internal/core/marketplace/invoice_test.go
new file mode 100644
index 000000000..1ebba4af6
--- /dev/null
+++ b/veza-backend-api/internal/core/marketplace/invoice_test.go
@@ -0,0 +1,113 @@
+package marketplace
+
+import (
+	"bytes"
+	"context"
+	"testing"
+
+	"github.com/google/uuid"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap"
+	"gorm.io/driver/sqlite"
+	"gorm.io/gorm"
+
+	"veza-backend-api/internal/models"
+)
+
+func setupInvoiceTestDB(t *testing.T) *gorm.DB {
+	db, err := gorm.Open(sqlite.Open(":memory:"), &gorm.Config{})
+	require.NoError(t, err)
+	require.NoError(t, db.AutoMigrate(
+		&models.User{},
+		&Product{},
+		&Order{},
+		&OrderItem{},
+	))
+	return db
+}
+
+func TestGenerateInvoice_Success(t *testing.T) {
+	db := setupInvoiceTestDB(t)
+	logger := zap.NewNop()
+	svc := NewService(db, logger, nil)
+
+	buyerID := uuid.New()
+	productID := uuid.New()
+	orderID := uuid.New()
+
+	require.NoError(t, db.Create(&models.User{ID: buyerID, Username: "buyer1", Email: "b@test.com"}).Error)
+	require.NoError(t, db.Create(&Product{ID: productID, SellerID: uuid.New(), Title: "Sample Track", Price: 9.99, ProductType: "track", Status: ProductStatusActive}).Error)
+	require.NoError(t, db.Create(&Order{
+		ID:          orderID,
+		BuyerID:     buyerID,
+		TotalAmount: 19.98,
+		Currency:    "EUR",
+		Status:      "completed",
+	}).Error)
+	require.NoError(t, db.Create(&OrderItem{ID: uuid.New(), OrderID: orderID, ProductID: productID, Price: 9.99}).Error)
+	require.NoError(t, db.Create(&OrderItem{ID: uuid.New(), OrderID: orderID, ProductID: productID, Price: 9.99}).Error)
+
+	pdf, err := svc.GenerateInvoice(context.Background(), orderID, buyerID)
+	require.NoError(t, err)
+	require.NotEmpty(t, pdf)
+	assert.True(t, bytes.HasPrefix(pdf, []byte("%PDF")), "PDF should start with %PDF")
+}
+
+func TestGenerateInvoice_WrongBuyer(t *testing.T) {
+	db := setupInvoiceTestDB(t)
+	logger := zap.NewNop()
+	svc := NewService(db, logger, nil)
+
+	buyerID := uuid.New()
+	otherBuyerID := uuid.New()
+	orderID := uuid.New()
+	productID := uuid.New()
+
+	require.NoError(t, db.Create(&models.User{ID: buyerID, Username: "buyer1", Email: "b@test.com"}).Error)
+	require.NoError(t, db.Create(&models.User{ID: otherBuyerID, Username: "other", Email: "o@test.com"}).Error)
+	require.NoError(t, db.Create(&Product{ID: productID, SellerID: uuid.New(), Title: "P", Price: 1, ProductType: "track", Status: ProductStatusActive}).Error)
+	require.NoError(t, db.Create(&Order{ID: orderID, BuyerID: buyerID, TotalAmount: 1, Currency: "EUR", Status: "completed"}).Error)
+	require.NoError(t, db.Create(&OrderItem{ID: uuid.New(), OrderID: orderID, ProductID: productID, Price: 1}).Error)
+
+	_, err := svc.GenerateInvoice(context.Background(), orderID, otherBuyerID)
+	require.Error(t, err)
+	assert.ErrorIs(t, err, ErrOrderNotFound)
+}
+
+func TestGenerateInvoice_OrderNotFound(t *testing.T) {
+	db := setupInvoiceTestDB(t)
+	logger := zap.NewNop()
+	svc := NewService(db, logger, nil)
+
+	_, err := svc.GenerateInvoice(context.Background(), uuid.New(), uuid.New())
+	require.Error(t, err)
+	assert.ErrorIs(t, err, ErrOrderNotFound)
+}
+
+func TestGenerateInvoice_WithDiscount(t *testing.T) {
+	db := setupInvoiceTestDB(t)
+	logger := zap.NewNop()
+	svc := NewService(db, logger, nil)
+
+	buyerID := uuid.New()
+	productID := uuid.New()
+	orderID := uuid.New()
+
+	require.NoError(t, db.Create(&models.User{ID: buyerID, Username: "buyer1", Email: "b@test.com"}).Error)
+	require.NoError(t, db.Create(&Product{ID: productID, SellerID: uuid.New(), Title: "Discounted", Price: 10, ProductType: "track", Status: ProductStatusActive}).Error)
+	require.NoError(t, db.Create(&Order{
+		ID:                   orderID,
+		BuyerID:              buyerID,
+		TotalAmount:          9.50,
+		Currency:             "EUR",
+		Status:               "completed",
+		DiscountAmountCents:  500,
+	}).Error)
+	require.NoError(t, db.Create(&OrderItem{ID: uuid.New(), OrderID: orderID, ProductID: productID, Price: 10}).Error)
+
+	pdf, err := svc.GenerateInvoice(context.Background(), orderID, buyerID)
+	require.NoError(t, err)
+	require.NotEmpty(t, pdf)
+	assert.True(t, bytes.HasPrefix(pdf, []byte("%PDF")), "PDF should start with %PDF")
+}