diff --git a/src/transactions/timeline.service.ts b/src/transactions/timeline.service.ts
index 5c584fe..aec763e 100644
--- a/src/transactions/timeline.service.ts
+++ b/src/transactions/timeline.service.ts
@@ -62,10 +62,8 @@ export class TimelineService {
     // Check for delays
     const now = new Date();
     const updatedMilestones = milestones.map(m => {
-      if (m.status === MilestoneStatus.PENDING && new Date(m.expectedDate) < now) {
-        return { ...m, isOverdue: true };
-      }
-      return { ...m, isOverdue: false };
+      const isOverdue = m.status === MilestoneStatus.PENDING && new Date(m.expectedDate) < now;
+      return { ...m, isOverdue };
     });
 
     return {
diff --git a/test/transactions/transactions.service.spec.ts b/test/transactions/transactions.service.spec.ts
index 175cc62..55e27a5 100644
--- a/test/transactions/transactions.service.spec.ts
+++ b/test/transactions/transactions.service.spec.ts
@@ -181,6 +181,67 @@ describe('TransactionsService', () => {
       }),
       include: expect.any(Object),
     });
+    mockPrismaService.user.findUnique
+      .mockResolvedValueOnce(null)
+      .mockResolvedValueOnce({
+        id: 'seller-1',
+        firstName: 'Seller',
+        lastName: 'One',
+        email: 'seller@example.com',
+      });
+
+    await expect(
+      service.createTransaction(
+        {
+          propertyId: 'property-1',
+          buyerId: 'missing-buyer',
+          sellerId: 'seller-1',
+          amount: 1000,
+          type: TransactionType.SALE,
+        },
+        {
+          sub: 'missing-buyer',
+          email: 'buyer@example.com',
+          role: UserRole.USER,
+          type: 'access',
+        },
+      ),
+    ).rejects.toBeInstanceOf(NotFoundException);
+  });
+
+  it('rejects invalid seller references', async () => {
+    mockPrismaService.property.findUnique.mockResolvedValue({
+      id: 'property-1',
+      title: 'Property',
+      address: '123 Main St',
+      ownerId: 'seller-1',
+    });
+    mockPrismaService.user.findUnique
+      .mockResolvedValueOnce({
+        id: 'buyer-1',
+        firstName: 'Buyer',
+        lastName: 'One',
+        email: 'buyer@example.com',
+      })
+      .mockResolvedValueOnce(null);
+
+    await expect(
+      service.createTransaction(
+        {
+          propertyId: 'property-1',
+          buyerId: 'buyer-1',
+          sellerId: 'missing-seller',
+          amount: 1000,
+          type: TransactionType.SALE,
+        },
+        {
+          sub: 'buyer-1',
+          email: 'buyer@example.com',
+          role: UserRole.USER,
+          type: 'access',
+        },
+      ),
+    ).rejects.toBeInstanceOf(NotFoundException);
   });
 
   it('rejects invalid property references', async () => {