Update posGateway.md documentation

- Additional refinements to status monitoring documentation
- Ensure consistent terminology and examples throughout

Author: PayManiRazor

documents/posGateway.md

@@ -319,6 +319,8 @@ class POSIntegration:
             print(f"Checkout initiated: {activity_id}")
 
             print("Checkout initiated successfully")
+
+            self.close_checkout(device_mode=device_mode)
 
             return {
                 "success": True,