function apply_tags_in_shopify( $user_id, $tags )

    $cust_array = array(
        'tags' => implode(',', $tags)
    );

    $info = array('customer' => $cust_array );

    $args = array(

        'headers' => array('Authorization' => 'Basic ' . base64_encode($credentials) ),
        'method' => 'PUT',
        'body' => json_encode( $info )

    );

    $response = wp_remote_get( '/admin/customers/#1234.json', $args );

}

add_action( 'wpf_tags_applied', 'apply_tags_in_shopify', 10, 2 );