PayPal\Api\RefundRequest::setInvoiceNumber PHP Method

The invoice number that is used to track this payment. Character length and limitations: 127 single-byte alphanumeric characters.

public setInvoiceNumber ( string $invoice_number )
$invoice_number	string

    public function setInvoiceNumber($invoice_number)
    {
        $this->invoice_number = $invoice_number;
        return $this;
    }

RefundRequest