Custom EE message shortcode (VAT_TOTAL)

<?php
function register_vat_shortcode( $shortcodes, EE_Shortcodes $lib ) {
    if ( $lib instanceof EE_Transaction_Shortcodes ) {
        $shortcodes['[VAT_PAID]'] = _('This calculates 20% of the total price, to find out how much of what was paid is VAT.');
    }

    return $shortcodes;
}
add_filter( 'FHEE__EE_Shortcodes__shortcodes', 'register_vat_shortcode', 10, 2 );

function register_vat_shortcode_parser( $parsed, $shortcode, $data, $extra_data, EE_Shortcodes $lib ) {
    if ( $lib instanceof EE_Transaction_Shortcodes ) {
        $transaction = $data->txn instanceof EE_Transaction ? $data->txn : null;
        $transaction = ! $transaction instanceof EE_Transaction && is_array( $extra_data ) &&  isset( $extra_data['data'] ) && $extra_data['data'] instanceof EE_Messages_Addressee ? $extra_data['data']->txn: $transaction;

        if ( $shortcode == '[VAT_PAID]' ) {
            $vat_total = $transaction->total() * 0.2;
            
            return ! empty($vat_total) ? EEH_Template::format_currency( $vat_total ) : '';
        }
    }

    return $parsed;
}
add_filter( 'FHEE__EE_Shortcodes__parser_after', 'register_vat_shortcode_parser', 10, 5 );