diff --git a/server/db/database.js b/server/db/database.js
index a0dbeed..30ea4ab 100644
--- a/server/db/database.js
+++ b/server/db/database.js
@@ -238,9 +238,12 @@ export default class DBAdapter {
                 'SELECT quantity FROM products WHERE id = ?', [productId]
             );
 
-            // TODO
-            if (!product || product.quantity < quantity){
-                return Promise.reject();
+            const productRow = product?.[0];
+            if (!productRow || productRow.quantity < quantity){
+                return Promise.reject({
+                    type: DB_USER_ERROR,
+                    error: new Error("Insufficient product quantity")
+                });
             }
 
             const result = await this.#dbClient.query(
@@ -249,7 +252,7 @@ export default class DBAdapter {
             );
 
             await this.#dbClient.query(
-                'UPDATE products SET quantity = quantity - ? WHERE id = >',
+                'UPDATE products SET quantity = quantity - ? WHERE id = ?',
                 [quantity, productId]
             );
 
@@ -267,37 +270,44 @@ export default class DBAdapter {
                 'SELECT product_id, quantity FROM order_items WHERE id = ?', [itemId]
             );
 
-            // TODO
-            if (!item){
-                return Promise.reject();
+            const itemRow = item?.[0];
+            if (!itemRow){
+                return Promise.reject({
+                    type: DB_USER_ERROR,
+                    error: new Error("Order item not found")
+                });
             }
 
-            const diff = quantity - item.quantity;
+            const diff = quantity - itemRow.quantity;
 
             if (diff > 0){
                 const product = await this.#dbClient.query(
-                'SELECT quantity FROM products WHERE id = ?', [item.productId]
+                    'SELECT quantity FROM products WHERE id = ?', [itemRow.product_id]
                 );
 
-                if (product.quantity < diff){
-                    return Promise.reject();
+                const productRow = product?.[0];
+                if (!productRow || productRow.quantity < diff){
+                    return Promise.reject({
+                        type: DB_USER_ERROR,
+                        error: new Error("Insufficient product quantity")
+                    });
                 }
                 
                 await this.#dbClient.query(
-                    'UPDATE products SET quantity = quantity - ? WHERE id = >',
-                    [diff, item.productId]
+                    'UPDATE products SET quantity = quantity - ? WHERE id = ?',
+                    [diff, itemRow.product_id]
                 );
             }
 
             if (diff < 0) {
                 await this.#dbClient.query(
-                    'UPDATE products SET quantity = quantity - ? WHERE id = >',
-                    [-diff, item.productId]
+                    'UPDATE products SET quantity = quantity + ? WHERE id = ?',
+                    [-diff, itemRow.product_id]
                 );                
             }
 
             await this.#dbClient.query(
-                'UPDATE order_items SET quantity = ? WHERE id = >',
+                'UPDATE order_items SET quantity = ? WHERE id = ?',
                 [quantity, itemId]
             );                
 
@@ -315,14 +325,17 @@ export default class DBAdapter {
                 'SELECT product_id, quantity FROM order_items WHERE id = ?', [itemId]
             );
 
-            // TODO
-            if (!item){
-                return Promise.reject();
+            const itemRow = item?.[0];
+            if (!itemRow){
+                return Promise.reject({
+                    type: DB_USER_ERROR,
+                    error: new Error("Order item not found")
+                });
             }
 
             await this.#dbClient.query(
-                'UPDATE products SET quantity = quantity + ? WHERE id = >',
-                [item.quantity, item.productId]
+                'UPDATE products SET quantity = quantity + ? WHERE id = ?',
+                [itemRow.quantity, itemRow.product_id]
             );
 
             await this.#dbClient.query(
@@ -344,13 +357,16 @@ export default class DBAdapter {
                 'SELECT id, order_id FROM order_items WHERE id = ?', [itemId]
             );
 
-            // TODO
-            if (!item){
-                return Promise.reject();
+            const itemRow = item?.[0];
+            if (!itemRow){
+                return Promise.reject({
+                    type: DB_USER_ERROR,
+                    error: new Error("Order item not found")
+                });
             }
 
             await this.#dbClient.query(
-                'UPDATE order_items SET order_id = ? WHERE id = >',
+                'UPDATE order_items SET order_id = ? WHERE id = ?',
                 [targetOrderId, itemId]
             );
 
@@ -360,4 +376,4 @@ export default class DBAdapter {
             return Promise.reject();
         }
     }
-}
\ No newline at end of file
+}
diff --git a/server/server.js b/server/server.js
index d5d2d26..6f71759 100644
--- a/server/server.js
+++ b/server/server.js
@@ -16,6 +16,8 @@ const {
     PASSWORD
 } = process.env;
 
+const appPort = Number(PORT) || 3000;
+
 const app = express();
 app.use(express.json());
 
@@ -240,9 +242,7 @@ app.put('/api/orders/:orderId/items/:itemId', async (req, res) => {
 app.delete('/api/orders/:orderId/items/:itemId', async (req, res) => {
     try {
         await adapter.deleteOrderItem(req.params.itemId);
-        res.statusCode = 204;
-        res.message = "OK";
-        res.json({message: "success"});
+        res.status(204).end();
     } catch (err){
         res.statusCode = 500;
         res.message = "WHOOPS";
@@ -283,11 +283,11 @@ app.use((req, res) => {
     res.status(404).json({ error: 'Invalid route' });
 });
 
-app.listen(3000, async() => {
+const server = app.listen(appPort, async() => {
     try {
         await adapter.connect();
-        console.log(`✅ Server running on port 3000`);
-        console.log(`📡 Local: http://localhost:3000`);
+        console.log(`✅ Server running on port ${appPort}`);
+        console.log(`📡 Local: http://localhost:${appPort}`);
     } catch(err){
         console.log("Shutting down application...");
         process.exit(100);
@@ -296,8 +296,8 @@ app.listen(3000, async() => {
 
 process.on('SIGTERM', () => {
     console.log("CLOSE APP");
-    app.close( async() => {
+    server.close(async () => {
         await adapter.disconnect();
         console.log("DB DISCONNECTED");
     });
-});
\ No newline at end of file
+});