public function processTransaction(array $transactionData, string $operation): ProcessInterface
    {
        // When hitting the process endpoint, we only need the transactionId and operation key/value pairs, and
        // optionally the transactionAmount if we are capturing a portion of the total amount.
        $transactionData = array_filter($transactionData + ['operation' => $operation], function ($k) {
            return in_array($k, ['transactionId', 'operation', 'transactionAmount']);
        }, ARRAY_FILTER_USE_KEY);

        $uri = $this->getUri('process', $this->getParameters($transactionData));
        /** @var ProcessInterface $response */
        $response = $this->performRequest((string) $uri);

        Assert::isInstanceOf($response, ProcessInterface::class, 'Invalid response');

        return $response;
    }