Reply To: Duplicate orders are created.

/**
 * Prevent duplicate order
 */
add_filter('woocommerce_defer_transactional_emails', '__return_true' );
add_action( 'woocommerce_after_checkout_validation', 'forbid2orders', 10, 2 );

function forbid2orders( $fields, $errors ){
	$c_user_email = $fields['billing_email'];
	$c_transient_key = 'create_order_'.$c_user_email;
	$create_order = true;
	if(false === ($c_transient_results = get_transient($c_transient_key))){
		$c_transient_results = $fields['billing_email'];
		set_transient($c_transient_key, $c_transient_results, 3 * MINUTE_IN_SECONDS );
	}else{
		if($c_transient_results == $fields['billing_email']){
			$errors->add( 'validation', 'An order has already been created.  Please check your <a href="/my-account/orders/">Orders</a> or wait a few minutes to place a new one.' );
			
		}
	}
}

I am pasting the snippet here as it didn’t let me upload a php file as an attachment