How do you add a user custom field into Woocommerce emails?

This is my code so far in functions.php

add_filter( 'woocommerce_email_order_meta_fields', 'custom_woocommerce_email_order_meta_fields', 10, 3 );

function custom_woocommerce_email_order_meta_fields( $fields, $sent_to_admin, $order ) {
    $fields['meta_key'] = array(
        'label' => __( 'Store number' ),
        'value' => get_user_meta( $user_id, 'wpcf-store-number', true ),
    );
    return $fields;
}

The user custom field is wpcf-store-number which is already in the database. All I need to do now is to show it in the order confirmation email / New order email.