diff --git a/backend/src/main/java/com/petshop/backend/dto/productsupplier/BulkDeleteProductSupplierRequest.java b/backend/src/main/java/com/petshop/backend/dto/productsupplier/BulkDeleteProductSupplierRequest.java
new file mode 100644
index 00000000..dfa95bb5
--- /dev/null
+++ b/backend/src/main/java/com/petshop/backend/dto/productsupplier/BulkDeleteProductSupplierRequest.java
@@ -0,0 +1,12 @@
+package com.petshop.backend.dto.productsupplier;
+
+import jakarta.validation.constraints.NotEmpty;
+import lombok.Data;
+
+import java.util.List;
+
+@Data
+public class BulkDeleteProductSupplierRequest {
+    @NotEmpty(message = "Keys list cannot be empty")
+    private List<ProductSupplierKey> keys;
+}
diff --git a/backend/src/main/java/com/petshop/backend/dto/productsupplier/ProductSupplierKey.java b/backend/src/main/java/com/petshop/backend/dto/productsupplier/ProductSupplierKey.java
index b86b6980..3826b39c 100644
--- a/backend/src/main/java/com/petshop/backend/dto/productsupplier/ProductSupplierKey.java
+++ b/backend/src/main/java/com/petshop/backend/dto/productsupplier/ProductSupplierKey.java
@@ -11,8 +11,3 @@ public class ProductSupplierKey {
     private Long supplierId;
 }
 
-@Data
-public class BulkDeleteProductSupplierRequest {
-    @NotEmpty(message = "Keys list cannot be empty")
-    private List<ProductSupplierKey> keys;
-}
diff --git a/backend/src/main/java/com/petshop/backend/dto/purchaseorder/PurchaseOrderResponse.java b/backend/src/main/java/com/petshop/backend/dto/purchaseorder/PurchaseOrderResponse.java
index 4a67865c..a7e68041 100644
--- a/backend/src/main/java/com/petshop/backend/dto/purchaseorder/PurchaseOrderResponse.java
+++ b/backend/src/main/java/com/petshop/backend/dto/purchaseorder/PurchaseOrderResponse.java
@@ -24,16 +24,16 @@ public class PurchaseOrderResponse {
     private List<PurchaseOrderItemResponse> items;
     private LocalDateTime createdAt;
     private LocalDateTime updatedAt;
-}
 
-@Data
-@NoArgsConstructor
-@AllArgsConstructor
-public class PurchaseOrderItemResponse {
-    private Long id;
-    private Long productId;
-    private String productName;
-    private Integer quantity;
-    private BigDecimal unitCost;
-    private BigDecimal subtotal;
+    @Data
+    @NoArgsConstructor
+    @AllArgsConstructor
+    public static class PurchaseOrderItemResponse {
+        private Long id;
+        private Long productId;
+        private String productName;
+        private Integer quantity;
+        private BigDecimal unitCost;
+        private BigDecimal subtotal;
+    }
 }
diff --git a/backend/src/main/java/com/petshop/backend/dto/refund/RefundItemRequest.java b/backend/src/main/java/com/petshop/backend/dto/refund/RefundItemRequest.java
new file mode 100644
index 00000000..f972407c
--- /dev/null
+++ b/backend/src/main/java/com/petshop/backend/dto/refund/RefundItemRequest.java
@@ -0,0 +1,15 @@
+package com.petshop.backend.dto.refund;
+
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Positive;
+import lombok.Data;
+
+@Data
+public class RefundItemRequest {
+    @NotNull(message = "Sale item ID is required")
+    private Long saleItemId;
+
+    @NotNull(message = "Quantity is required")
+    @Positive(message = "Quantity must be positive")
+    private Integer quantity;
+}
diff --git a/backend/src/main/java/com/petshop/backend/dto/refund/RefundRequest.java b/backend/src/main/java/com/petshop/backend/dto/refund/RefundRequest.java
index 61ec7b3f..1abf9c23 100644
--- a/backend/src/main/java/com/petshop/backend/dto/refund/RefundRequest.java
+++ b/backend/src/main/java/com/petshop/backend/dto/refund/RefundRequest.java
@@ -16,13 +16,3 @@ public class RefundRequest {
 
     private String refundReason;
 }
-
-@Data
-class RefundItemRequest {
-    @NotNull(message = "Sale item ID is required")
-    private Long saleItemId;
-
-    @NotNull(message = "Quantity is required")
-    @Positive(message = "Quantity must be positive")
-    private Integer quantity;
-}
diff --git a/backend/src/main/java/com/petshop/backend/dto/sale/SaleItemRequest.java b/backend/src/main/java/com/petshop/backend/dto/sale/SaleItemRequest.java
new file mode 100644
index 00000000..60d5596e
--- /dev/null
+++ b/backend/src/main/java/com/petshop/backend/dto/sale/SaleItemRequest.java
@@ -0,0 +1,15 @@
+package com.petshop.backend.dto.sale;
+
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Positive;
+import lombok.Data;
+
+@Data
+public class SaleItemRequest {
+    @NotNull(message = "Product ID is required")
+    private Long productId;
+
+    @NotNull(message = "Quantity is required")
+    @Positive(message = "Quantity must be positive")
+    private Integer quantity;
+}
diff --git a/backend/src/main/java/com/petshop/backend/dto/sale/SaleRequest.java b/backend/src/main/java/com/petshop/backend/dto/sale/SaleRequest.java
index 56a7c71d..220aaa39 100644
--- a/backend/src/main/java/com/petshop/backend/dto/sale/SaleRequest.java
+++ b/backend/src/main/java/com/petshop/backend/dto/sale/SaleRequest.java
@@ -26,13 +26,3 @@ public class SaleRequest {
 
     private String notes;
 }
-
-@Data
-class SaleItemRequest {
-    @NotNull(message = "Product ID is required")
-    private Long productId;
-
-    @NotNull(message = "Quantity is required")
-    @Positive(message = "Quantity must be positive")
-    private Integer quantity;
-}
diff --git a/backend/src/main/java/com/petshop/backend/service/PurchaseOrderService.java b/backend/src/main/java/com/petshop/backend/service/PurchaseOrderService.java
index 1e9c61f0..fa5d9859 100644
--- a/backend/src/main/java/com/petshop/backend/service/PurchaseOrderService.java
+++ b/backend/src/main/java/com/petshop/backend/service/PurchaseOrderService.java
@@ -1,7 +1,7 @@
 package com.petshop.backend.service;
 
-import com.petshop.backend.dto.purchaseorder.PurchaseOrderItemResponse;
 import com.petshop.backend.dto.purchaseorder.PurchaseOrderResponse;
+import com.petshop.backend.dto.purchaseorder.PurchaseOrderResponse.PurchaseOrderItemResponse;
 import com.petshop.backend.entity.PurchaseOrder;
 import com.petshop.backend.entity.PurchaseOrderItem;
 import com.petshop.backend.exception.ResourceNotFoundException;