Wordpress kayıt formuna ek alanlar ekleme

<?php
add_action( 'register_form', 'iskendercnr_register_form' );
function iskendercnr_register_form() {
//1- forma alan ekle
    $vergi_no = ( ! empty( $_POST['vergi_no'] ) ) ? $_POST['vergi_no'] : '';
    $vergi_daire = ( ! empty( $_POST['vergi_daire'] ) ) ? $_POST['vergi_daire'] : '';
    $sirket_unvan = ( ! empty( $_POST['sirket_unvan'] ) ) ? $_POST['sirket_unvan'] : '';
        ?>
        <p>
            <label for="vergi_no"><?php _e( 'Vergi Numarası', 'mydomain' ) ?><br />
                <input type="text" name="vergi_no" id="vergi_no" class="input" value="<?php echo esc_attr(  $vergi_no  ); ?>" size="25" /></label>
        </p>
        <p>
            <label for="vergi_daire"><?php _e( 'Vergi Dairesi', 'mydomain' ) ?><br />
                <input type="text" name="vergi_daire" id="vergi_daire" class="input" value="<?php echo esc_attr(  $vergi_daire  ); ?>" size="25" /></label>
        </p>
        <p>
            <label for="sirket_unvan"><?php _e( 'Şirket Ünvanı', 'mydomain' ) ?><br />
                <input type="text" name="sirket_unvan" id="sirket_unvan" class="input" value="<?php echo esc_attr(  $sirket_unvan  ); ?>" size="25" /></label>
        </p>
        <?php
    }

    //2. validation ekle
    add_filter( 'registration_errors', 'iskendercnr_registration_errors', 10, 3 );
    function iskendercnr_registration_errors( $errors, $sanitized_user_login, $user_email ) {

        if ( !empty( $_POST['vergi_no'] ) && trim( $_POST['vergi_no'] ) == '' || !empty( $_POST['vergi_daire'] ) && trim( $_POST['vergi_daire'] ) == '' || !empty( $_POST['sirket_unvan'] ) && trim( $_POST['sirket_unvan'] ) == '') {
        $errors->add( 'input_error', sprintf('<strong>%s</strong>: %s',__( 'ERROR', 'mydomain' ),__( 'Alanları Boş Bırakmayın.', 'mydomain' ) ) );

        }

        return $errors;
    }

    //3. dataları kaydet
    add_action( 'user_register', 'iskendercnr_user_register' );
    function iskendercnr_user_register( $user_id ) {

        if ( ! empty( $_POST['vergi_no'] ) && ! empty( $_POST['vergi_daire'] ) && ! empty( $_POST['sirket_unvan'] )) {
            update_user_meta( $user_id, 'vergi_no', $_POST['first_name'] );
            update_user_meta( $user_id, 'vergi_daire', $_POST['vergi_daire'] );
            update_user_meta( $user_id, 'sirket_unvan', $_POST['sirket_unvan'] );
        }
    }