Braintree\TransactionGateway::submitForPartialSettlement PHP Method

    public function submitForPartialSettlement($transactionId, $amount, $attribs = [])
    {
        $this->_validateId($transactionId);
        Util::verifyKeys(self::submitForSettlementSignature(), $attribs);
        $attribs['amount'] = $amount;
        $path = $this->_config->merchantPath() . '/transactions/' . $transactionId . '/submit_for_partial_settlement';
        $response = $this->_http->post($path, ['transaction' => $attribs]);
        return $this->_verifyGatewayResponse($response);
    }