diff --git a/lib/services/entity-sync.ts b/lib/services/entity-sync.ts
index 12b3b53..e4b9bbb 100644
--- a/lib/services/entity-sync.ts
+++ b/lib/services/entity-sync.ts
@@ -18,6 +18,7 @@ import {
   buildContractsFilter,
   buildProjectsFilter,
   buildTimeEntriesFilter,
+  buildBillingItemsFilter,
   getTableName 
 } from '../utils/sync-helpers';
 import { createSyncLogger, SyncPhase, categorizeError } from '../utils/sync-logger';
@@ -112,6 +113,9 @@ export class EntitySyncService {
         } else if (entity === EntityType.TIME_ENTRIES) {
           filters.push(...buildTimeEntriesFilter(yearsBack));
           entityLogger.info(`Full sync with dateWorked filter for last ${yearsBack} years`);
+        } else if (entity === EntityType.BILLING_ITEMS) {
+          filters.push(...buildBillingItemsFilter(yearsBack));
+          entityLogger.info(`Full sync with itemDate filter for last ${yearsBack} years`);
         } else {
           // Add active filter if applicable
           const activeFilter = buildActiveFilter(entity);
@@ -270,6 +274,32 @@ export class EntitySyncService {
         }
       }
 
+      // Validate project foreign keys for tasks
+      if (entity === EntityType.TASKS) {
+        const initialCount = mappedRecords.length;
+        
+        // Get all valid project IDs from database
+        const validProjectIds = await this.getValidProjectIds();
+        
+        // Filter tasks with invalid project references
+        mappedRecords = mappedRecords.map(task => {
+          // Set invalid project IDs to null instead of filtering out the entire task
+          if (task.project_id && !validProjectIds.has(task.project_id)) {
+            entityLogger.debug(`Invalid project_id, setting to null`, {
+              taskId: task.id,
+              invalidProjectId: task.project_id,
+            });
+            task.project_id = null;
+          }
+          return task;
+        });
+        
+        const nullifiedCount = initialCount - mappedRecords.filter(t => t.project_id).length;
+        if (nullifiedCount > 0) {
+          entityLogger.warn('Nullified invalid project references', { nullifiedCount });
+        }
+      }
+
       entityLogger.info('Successfully mapped records', { mappedCount: mappedRecords.length });
 
       // Bulk upsert to PostgreSQL
@@ -547,6 +577,24 @@ export class EntitySyncService {
     }
   }
 
+  /**
+   * Get all valid project IDs from the database
+   * Used to validate foreign key references before insert
+   * @returns Set of valid project IDs
+   */
+  private async getValidProjectIds(): Promise<Set<number>> {
+    try {
+      const query = 'SELECT id FROM projects WHERE is_deleted = false';
+      const result = await postgresClient.query<{ id: number }>(query);
+      return new Set(result.rows.map(row => row.id));
+    } catch (error) {
+      const err = error instanceof Error ? error : new Error(String(error));
+      this.logger.error('Failed to fetch valid project IDs', {}, err);
+      // Return empty set on error - will cause all project IDs to be nullified
+      return new Set();
+    }
+  }
+
   /**
    * Calculate monthly date chunks for a given time period
    * @param yearsBack Number of years to look back
diff --git a/lib/utils/sync-helpers.ts b/lib/utils/sync-helpers.ts
index 423abf0..fc80001 100644
--- a/lib/utils/sync-helpers.ts
+++ b/lib/utils/sync-helpers.ts
@@ -332,6 +332,30 @@ export function buildTimeEntriesFilter(yearsBack: number = 2): Array<{ field: st
   ];
 }
 
+/**
+ * Build special filter for billing items (requires filter)
+ * @param yearsBack Number of years to look back (default: 2)
+ * @returns Query filter array for billing items
+ */
+export function buildBillingItemsFilter(yearsBack: number = 2): Array<{ field: string; op: string; value: any }> {
+  // BillingItems API requires a filter. Use itemDate to limit the range
+  // Calculate date from X years ago
+  const cutoffDate = new Date();
+  const millisecondsPerYear = 365.25 * 24 * 60 * 60 * 1000;
+  const millisecondsBack = yearsBack * millisecondsPerYear;
+  cutoffDate.setTime(cutoffDate.getTime() - millisecondsBack);
+
+  console.log(`BillingItems filter: itemDate >= ${cutoffDate.toISOString()} (${yearsBack} years back)`);
+
+  return [
+    {
+      field: 'itemDate',
+      op: 'gte',
+      value: cutoffDate.toISOString(),
+    },
+  ];
+}
+
 /**
  * Calculate estimated sync duration based on record count
  * @param recordCount Number of records to sync