payment_amount_human_readable() has been removed

payment_amount_human_readable() has been removed in favor of Currency's localized amount formatting.

7.x-1.x:

$amount = 123.45;
$currency_code = 'EUR';
$formatted = payment_amount_human_readable($amount, $currency_code);

8.x-2.x:

$amount = 123.45;
$currency_code = 'EUR';
$currency = entity_load('currency', $currency_code);
$formatted = $currency->format($amount);