I really don't know if we have some rules to create Mercosul/Brazilian license plate, but I think that we should keep support for both (after 2024 we can drop Brazilian support since Brazil will only use Mercosul format).

Módulos afetados:
public/assets/js/credito.js
public/assets/js/boleto.js
public/assets/js/sessao.js

Atual:

$('.msg').html('Ocorreu um erro: ' + res.error + ' ' + res.message)

Library:
app/Libraries/PagSeguro.php

Atual:

$retorno = [
    'error'     =>  $std->error->code,
    'message'   => $std->error->message
 ];