code: public CoinbaseTransaction completeCoinbaseRequest(String transactionId) throws IOException {
  
      final CoinbaseTransaction response =
          coinbase.completeRequest(
              transactionId,
              exchange.getExchangeSpecification().getApiKey(),
              signatureCreator,
              exchange.getNonceFactory());
      return handleResponse(response);
    }
docs: Authenticated resource which lets a user complete a money request. Money requests can only be
  completed by the sender (not the recipient). Remember that the sender in this context is the
  user who is sending money (not sending the request itself).
  
  @param transactionId
  @return The {@code CoinbaseTransaction} representing the completed {@code
  CoinbaseSendMoneyRequest}.
  @throws IOException
  @see <a
  href="https://coinbase.com/api/doc/1.0/transactions/complete_request.html">coinbase.com/api/doc/1.0/transactions/complete_request.html
  </a>