function currency_exchange(){
    $valid_coins = array("usd", "pen", "ars", "bob", "brl", "cop", "eur", "clp", "bsf");

    $from     = $this->input->post('from');
    $to       = $this->input->post('to');
    $amount   = (int) $this->input->post('amount');

    $validate_from = in_array($from, $valid_coins);
    $validate_to   = in_array($to, $valid_coins);

    if($validate_from and $validate_to){
        $response = $this->inkapay_model->getCalcSendMoney($from ,$to , $amount);
        echo json_encode($response);
    }else{
        $response = array("error"=>"invalid coin");
        echo json_encode($response);
    }
}