Source code for https://formindable-masterminds.com/add-currency-to-formidables-global-list/

add_currency.php

<?php

apply_filters( 'frm_currencies', 'add_currency' );
function add_currency( $currencies ) {
    /* this adds the Eastern Caribbean dollar to Formidable's currency list */ 
    $currencies['XCD']= array(
        'name' => __( 'Eastern Caribbean dollar', 'formidable-pro' ),
        'symbol_left' => '$',
        'symbol_right' => '',
        'symbol_padding' => ' ',
        'thousand_separator' => ',',
        'decimal_separator' => '.',
        'decimals' => 2,
    );
    return $currencies;
}