diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4fc19ae..8315e72 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,43 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [2.22.21] - 2025-11-20
+
+### 🐛 Bug Fixes
+
+**Fix Empty Settings Object Validation Error (#431)**
+
+Fixed critical bug where `n8n_update_partial_workflow` tool failed with "request/body must NOT have additional properties" error when workflows had no settings or only non-whitelisted settings properties.
+
+#### Root Cause
+- `cleanWorkflowForUpdate()` in `src/services/n8n-validation.ts` was sending empty `settings: {}` objects to the n8n API
+- n8n API rejects empty settings objects as "additional properties" violation
+- Issue occurred when:
+  - Workflow had no settings property
+  - Workflow had only non-whitelisted settings (e.g., only `callerPolicy`)
+
+#### Changes
+- **Primary Fix**: Modified `cleanWorkflowForUpdate()` to delete `settings` property when empty after filtering
+  - Instead of sending `settings: {}`, the property is now omitted entirely
+  - Added safeguards in lines 193-199 and 201-204
+- **Secondary Fix**: Enhanced `applyUpdateSettings()` in `workflow-diff-engine.ts` to prevent creating empty settings objects
+  - Only creates/updates settings if operation provides actual properties
+- **Test Updates**: Fixed 3 incorrect tests that expected empty settings objects
+  - Updated to expect settings property to be omitted instead
+  - Added 2 new comprehensive tests for edge cases
+
+#### Testing
+- All 75 unit tests in `n8n-validation.test.ts` passing
+- New tests cover:
+  - Workflows with no settings → omits property
+  - Workflows with only non-whitelisted settings → omits property
+  - Workflows with mixed settings → keeps only whitelisted properties
+
+**Related Issues**: #431, #248 (n8n API design limitation)
+**Related n8n Issue**: n8n-io/n8n#19587 (closed as NOT_PLANNED - MCP server issue)
+
+Conceived by Romuald Członkowski - https://www.aiadvisors.pl/en
+
 ## [2.22.20] - 2025-11-19
 
 ### 🔄 Dependencies
diff --git a/package.json b/package.json
index 37d177b..26a2dd3 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "n8n-mcp",
-  "version": "2.22.20",
+  "version": "2.22.21",
   "description": "Integration between n8n workflow automation and Model Context Protocol (MCP)",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
diff --git a/src/services/n8n-validation.ts b/src/services/n8n-validation.ts
index 439a017..f0aa22e 100644
--- a/src/services/n8n-validation.ts
+++ b/src/services/n8n-validation.ts
@@ -189,10 +189,18 @@ export function cleanWorkflowForUpdate(workflow: Workflow): Partial<Workflow> {
         filteredSettings[key] = (cleanedWorkflow.settings as any)[key];
       }
     }
-    cleanedWorkflow.settings = filteredSettings;
+
+    // Only include settings if it has properties after filtering
+    // n8n API rejects empty settings objects
+    if (Object.keys(filteredSettings).length > 0) {
+      cleanedWorkflow.settings = filteredSettings;
+    } else {
+      delete cleanedWorkflow.settings;
+    }
   } else {
-    // No settings provided - use empty object for safety
-    cleanedWorkflow.settings = {};
+    // No settings provided - remove the property entirely
+    // n8n API rejects empty settings objects
+    delete cleanedWorkflow.settings;
   }
 
   return cleanedWorkflow;
diff --git a/src/services/workflow-diff-engine.ts b/src/services/workflow-diff-engine.ts
index 9b78e95..3538dd8 100644
--- a/src/services/workflow-diff-engine.ts
+++ b/src/services/workflow-diff-engine.ts
@@ -861,10 +861,14 @@ export class WorkflowDiffEngine {
 
   // Metadata operation appliers
   private applyUpdateSettings(workflow: Workflow, operation: UpdateSettingsOperation): void {
-    if (!workflow.settings) {
-      workflow.settings = {};
+    // Only create/update settings if operation provides actual properties
+    // This prevents creating empty settings objects that would be rejected by n8n API
+    if (operation.settings && Object.keys(operation.settings).length > 0) {
+      if (!workflow.settings) {
+        workflow.settings = {};
+      }
+      Object.assign(workflow.settings, operation.settings);
     }
-    Object.assign(workflow.settings, operation.settings);
   }
 
   private applyUpdateName(workflow: Workflow, operation: UpdateNameOperation): void {
diff --git a/tests/unit/services/n8n-validation.test.ts b/tests/unit/services/n8n-validation.test.ts
index 1d5e9e5..b0e5cdc 100644
--- a/tests/unit/services/n8n-validation.test.ts
+++ b/tests/unit/services/n8n-validation.test.ts
@@ -367,7 +367,7 @@ describe('n8n-validation', () => {
         expect(cleaned.name).toBe('Test Workflow');
       });
 
-      it('should add empty settings object for cloud API compatibility', () => {
+      it('should omit settings property when no settings provided (Issue #431)', () => {
         const workflow = {
           name: 'Test Workflow',
           nodes: [],
@@ -375,7 +375,7 @@ describe('n8n-validation', () => {
         } as any;
 
         const cleaned = cleanWorkflowForUpdate(workflow);
-        expect(cleaned.settings).toEqual({});
+        expect(cleaned).not.toHaveProperty('settings');
       });
 
       it('should filter settings to safe properties to prevent API errors (Issue #248 - final fix)', () => {
@@ -467,7 +467,48 @@ describe('n8n-validation', () => {
         } as any;
 
         const cleaned = cleanWorkflowForUpdate(workflow);
-        expect(cleaned.settings).toEqual({});
+        expect(cleaned).not.toHaveProperty('settings');
+      });
+
+      it('should omit settings when only non-whitelisted properties exist (Issue #431)', () => {
+        const workflow = {
+          name: 'Test Workflow',
+          nodes: [],
+          connections: {},
+          settings: {
+            callerPolicy: 'workflowsFromSameOwner' as const, // Filtered out
+            timeSavedPerExecution: 5, // Filtered out (UI-only)
+            someOtherProperty: 'value', // Filtered out
+          },
+        } as any;
+
+        const cleaned = cleanWorkflowForUpdate(workflow);
+        // All properties were filtered out, so settings should not exist
+        // to avoid "must NOT have additional properties" API error
+        expect(cleaned).not.toHaveProperty('settings');
+      });
+
+      it('should preserve whitelisted settings when mixed with non-whitelisted (Issue #431)', () => {
+        const workflow = {
+          name: 'Test Workflow',
+          nodes: [],
+          connections: {},
+          settings: {
+            executionOrder: 'v1' as const, // Whitelisted
+            callerPolicy: 'workflowsFromSameOwner' as const, // Filtered out
+            timezone: 'America/New_York', // Whitelisted
+            someOtherProperty: 'value', // Filtered out
+          },
+        } as any;
+
+        const cleaned = cleanWorkflowForUpdate(workflow);
+        // Should keep only whitelisted properties
+        expect(cleaned.settings).toEqual({
+          executionOrder: 'v1',
+          timezone: 'America/New_York'
+        });
+        expect(cleaned.settings).not.toHaveProperty('callerPolicy');
+        expect(cleaned.settings).not.toHaveProperty('someOtherProperty');
       });
     });
   });
@@ -1346,7 +1387,7 @@ describe('n8n-validation', () => {
       expect(forUpdate).not.toHaveProperty('active');
       expect(forUpdate).not.toHaveProperty('tags');
       expect(forUpdate).not.toHaveProperty('meta');
-      expect(forUpdate.settings).toEqual({}); // Settings replaced with empty object for API compatibility
+      expect(forUpdate).not.toHaveProperty('settings'); // Settings omitted when not present (Issue #431)
       expect(validateWorkflowStructure(forUpdate)).toEqual([]);
     });
   });