diff --git a/src/services/flyerDataTransformer.test.ts b/src/services/flyerDataTransformer.test.ts
index 39821106..00fc5c00 100644
--- a/src/services/flyerDataTransformer.test.ts
+++ b/src/services/flyerDataTransformer.test.ts
@@ -21,6 +21,11 @@ describe('FlyerDataTransformer', () => {
   beforeEach(() => {
     vi.clearAllMocks();
     transformer = new FlyerDataTransformer();
+    // Stub environment variables to ensure consistency and predictability.
+    // Prioritize FRONTEND_URL to match the updated service logic.
+    vi.stubEnv('FRONTEND_URL', 'http://localhost:3000');
+    vi.stubEnv('BASE_URL', ''); // Ensure this is not used to confirm priority logic
+    vi.stubEnv('PORT', '');     // Ensure this is not used
 
     // Provide a default mock implementation for generateFlyerIcon
     vi.mocked(generateFlyerIcon).mockResolvedValue('icon-flyer-page-1.webp');
@@ -70,6 +75,9 @@ describe('FlyerDataTransformer', () => {
       mockLogger,
     );
 
+    // Dynamically construct the expected base URL, mirroring the logic in the transformer.
+    const expectedBaseUrl = `http://localhost:3000`;
+
     // Assert
     // 0. Check logging
     expect(mockLogger.info).toHaveBeenCalledWith(
@@ -83,8 +91,8 @@ describe('FlyerDataTransformer', () => {
     // 1. Check flyer data
     expect(flyerData).toEqual({
       file_name: originalFileName,
-      image_url: `http://localhost:3000/flyer-images/flyer-page-1.jpg`,
-      icon_url: `http://localhost:3000/flyer-images/icons/icon-flyer-page-1.webp`,
+      image_url: `${expectedBaseUrl}/flyer-images/flyer-page-1.jpg`,
+      icon_url: `${expectedBaseUrl}/flyer-images/icons/icon-flyer-page-1.webp`,
       checksum,
       store_name: 'Test Store',
       valid_from: '2024-01-01',
@@ -151,6 +159,9 @@ describe('FlyerDataTransformer', () => {
       mockLogger,
     );
 
+    // Dynamically construct the expected base URL, mirroring the logic in the transformer.
+    const expectedBaseUrl = `http://localhost:3000`;
+
     // Assert
     // 0. Check logging
     expect(mockLogger.info).toHaveBeenCalledWith(
@@ -167,8 +178,8 @@ describe('FlyerDataTransformer', () => {
     expect(itemsForDb).toHaveLength(0);
     expect(flyerData).toEqual({
       file_name: originalFileName,
-      image_url: `http://localhost:3000/flyer-images/another.png`,
-      icon_url: `http://localhost:3000/flyer-images/icons/icon-another.webp`,
+      image_url: `${expectedBaseUrl}/flyer-images/another.png`,
+      icon_url: `${expectedBaseUrl}/flyer-images/icons/icon-another.webp`,
       checksum,
       store_name: 'Unknown Store (auto)', // Should use fallback
       valid_from: null,
diff --git a/src/services/flyerDataTransformer.ts b/src/services/flyerDataTransformer.ts
index cfa0a3a1..f3feec59 100644
--- a/src/services/flyerDataTransformer.ts
+++ b/src/services/flyerDataTransformer.ts
@@ -76,7 +76,7 @@ export class FlyerDataTransformer {
       }
 
       // Construct proper URLs including protocol and host to satisfy DB constraints
-      const rawBaseUrl = process.env.BASE_URL || `http://localhost:${process.env.PORT || 3000}`;
+      const rawBaseUrl = process.env.FRONTEND_URL || process.env.BASE_URL || `http://localhost:${process.env.PORT || 3000}`;
       // Normalize base URL by removing any trailing slash to prevent double slashes in the final URL,
       // and replace the strict `new URL()` constructor to prevent exceptions in test environments.
       const baseUrl = rawBaseUrl.endsWith('/') ? rawBaseUrl.slice(0, -1) : rawBaseUrl;
@@ -91,7 +91,10 @@ export class FlyerDataTransformer {
         valid_to: extractedData.valid_to,
         store_address: extractedData.store_address, // The number of items is now calculated directly from the transformed data.
         item_count: itemsForDb.length,
-        uploaded_by: userId,
+        // Defensively handle the userId. An empty string ('') is not a valid UUID,
+        // but `null` is. This ensures that any falsy value for userId (undefined, null, '')
+        // is converted to `null` for the database, preventing a 22P02 error.
+        uploaded_by: userId || null,
         status: needsReview ? 'needs_review' : 'processed',
       };
 
diff --git a/src/tests/integration/gamification.integration.test.ts b/src/tests/integration/gamification.integration.test.ts
index 1af3c4e7..b01bf27f 100644
--- a/src/tests/integration/gamification.integration.test.ts
+++ b/src/tests/integration/gamification.integration.test.ts
@@ -162,6 +162,6 @@ describe('Gamification Flow Integration Test', () => {
         firstUploadAchievement!.points_value,
       );
     },
-    120000, // Increase timeout to 120 seconds for this long-running test
+    240000, // Increase timeout to 240s to match other long-running processing tests
   );
 });
\ No newline at end of file