Use StopDBCluster with an AWS SDK

    /**
     * Stops an Amazon Neptune DB cluster.
     *
     * @param clusterIdentifier the unique identifier of the DB cluster to be stopped
     */
    public CompletableFuture<StopDbClusterResponse> stopDBClusterAsync(String clusterIdentifier) {
        StopDbClusterRequest clusterRequest = StopDbClusterRequest.builder()
                .dbClusterIdentifier(clusterIdentifier)
                .build();

        return getAsyncClient().stopDBCluster(clusterRequest)
                .whenComplete((response, error) -> {
                    if (error != null) {
                        Throwable cause = error.getCause() != null ? error.getCause() : error;

                        if (cause instanceof ResourceNotFoundException) {
                            throw (ResourceNotFoundException) cause;
                        }

                        throw new RuntimeException("Failed to stop DB cluster: " + cause.getMessage(), cause);
                    } else {
                        logger.info("DB Cluster stopped: " + clusterIdentifier);
                    }
                });
    }

def stop_db_cluster(neptune_client, cluster_identifier: str):
    """
    Stops an Amazon Neptune DB cluster and waits until it's fully stopped.

    Args:
        neptune_client (boto3.client): The Neptune client.
        cluster_identifier (str): The DB cluster identifier.

    Raises:
        ClientError: For AWS API errors (e.g., resource not found).
        RuntimeError: If the cluster doesn't stop within the timeout.
    """
    try:
        neptune_client.stop_db_cluster(DBClusterIdentifier=cluster_identifier)
    except ClientError as err:
        code = err.response["Error"]["Code"]
        message = err.response["Error"]["Message"]

        if code == "AccessDeniedException":
            print("Access denied. Please ensure you have the necessary permissions.")
        else:
            print(f"Couldn't stop DB cluster. Here's why: {code}: {message}")
        raise

    start_time = time.time()
    paginator = neptune_client.get_paginator('describe_db_clusters')

    while True:
        try:
            pages = paginator.paginate(DBClusterIdentifier=cluster_identifier)
            clusters = []
            for page in pages:
                clusters.extend(page.get('DBClusters', []))
        except ClientError as err:
            code = err.response["Error"]["Code"]
            message = err.response["Error"]["Message"]

            if code == "DBClusterNotFound":
                print(f"Cluster '{cluster_identifier}' not found while polling. It may have been deleted.")
            else:
                print(f"Couldn't describe DB cluster. Here's why: {code}: {message}")
            raise

        status = clusters[0].get('Status') if clusters else None
        elapsed = time.time() - start_time

        print(f"\rElapsed: {int(elapsed)}s – Cluster status: {status}", end="", flush=True)

        if status and status.lower() == 'stopped':
            print(f"\nCluster '{cluster_identifier}' is now stopped.")
            return

        if elapsed > TIMEOUT_SECONDS:
            raise RuntimeError(f"Timeout waiting for cluster '{cluster_identifier}' to stop.")

        time.sleep(POLL_INTERVAL_SECONDS)