add-idoklad-invoice-exchange-rate.php

<?php

$ExchangeRate = apply_filters( 'idoklad_exchange_rate', false, $order_id );
if( $ExchangeRate != false ){
  $data['ExchangeRate'] = $ExchangeRate;
}

$ExchangeRateAmount = apply_filters( 'idoklad_exchange_rate_amount', false, $order_id );
if( $ExchangeRateAmount != false ){
  $data['ExchangeRateAmount'] = $ExchangeRateAmount;
}

add_filter( 'idoklad_exchange_rate', 'toret_add_idoklad_exchange_rate', 10, 2 );
function toret_add_idoklad_exchange_rate( $rate, $order_id ){
  
  return 25; //Decimal number

}