src/Message/AbstractRequest.php
protected function getInvoiceData()
    {
        $data = array();
        $data['Amount'] = $this->getAmount();
        if ($this->getDescription()) {
            $data['OrderDescription'] = $this->getDescription();
        }
        return $data;
    }
protected function getInvoiceData()
    {
        $data = array();
        $data['Amount'] = $this->getAmount();
        if ($this->getDescription()) {
            $data['OrderDescription'] = $this->getDescription();
        }
        return $data;
    }
Get the invoice data

@return array