Unavailable Serverless Db Engine Mode Error

I'm facing following issue when creating Serverless Aurora Postgres 14.5 Cluster using AWS CDK. I've also tested out different versions such as 15.2, 14.6, 14.7. Error: "The engine mode serverless you requested is currently unavailable. "

self.aurora_serverless_db = rds.ServerlessCluster(
            self,
            "AuroraServerlessCluster",
            engine=rds.DatabaseClusterEngine.aurora_postgres(version=rds.AuroraPostgresEngineVersion.VER_14_5),
            vpc=self.vpc,
            vpc_subnets=ec2.SubnetSelection(subnet_type=ec2.SubnetType.PRIVATE_ISOLATED),
            default_database_name="serverless_db",
            backup_retention=Duration.days(1), 
            deletion_protection=True,
            enable_data_api=True, 
            parameter_group=rds.ParameterGroup.from_parameter_group_name( 
                self,
                "AuroraDBParameterGroup",
                "default.aurora-postgresql14"  
            ),
            scaling=rds.ServerlessScalingOptions(
                auto_pause=Duration.minutes(30),
                # Shutdown after minutes of inactivity to save costs
                min_capacity=rds.AuroraCapacityUnit.ACU_2,
                max_capacity=rds.AuroraCapacityUnit.ACU_4
            ),
        )

All is working well with engine = rds.DatabaseClusterEngine.AURORA_POSTGRES and parameter_group ="default.aurora-postgresql10"