Add currency code to the checkout display in Event Espresso 4.

add_currency_code_spco.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

function my_ee_add_currency_checkout() {
  wp_add_inline_script( 
    'single_page_checkout',
    'jQuery( document ).one( "ajaxStop", function() {
        jQuery("#spco-payment-info-table")
        .find(".spco-grand-total td:contains(\'$\')")
        .append("<span>(USD)</span>");
    } );'
  );
}
add_action( 'wp_enqueue_scripts', 'my_ee_add_currency_checkout', 11 );