RestHandler::getSystemParams

private function getSystemParams(Payment $payment): array
{
	$params['BX_SYSTEM_PARAMS'] = [
		'RETURN_URL' => $this->service->getContext()->getUrl(),
		'PAYSYSTEM_ID' => $this->service->getField('ID'),
		'PAYMENT_ID' => $payment->getId(),
		'SUM' => $payment->getSum(),
		'CURRENCY' => $payment->getField('CURRENCY'),
	];

	$invoiceId = $payment->getField('PS_INVOICE_ID');
	if (isset($invoiceId))
	{
		$params['BX_SYSTEM_PARAMS']['EXTERNAL_PAYMENT_ID'] = $invoiceId;
	}

	return $params;
}