gistfile1.txt

  const makeTransaction = (amount, nonceFromTheClient) => {
    gateway.transaction.sale({
      amount: amount,
      paymentMethodNonce: nonceFromTheClient,
      options: {
        submitForSettlement: true
      }
    }, function(err, result) {
      if (result.success) {
        logger.info('[Braintree] Nouvelle transaction: %s', result.transaction.id);
        knex('commande')
          .insert({
            userid: req.sessionID,
            status: result.transaction.status,
            mode: result.transaction.paymentInstrumentType,
            amount: result.transaction.amount,
            cardtype: result.transaction.creditCard.cardType,
            number: result.transaction.creditCard.maskedNumber,
            expirationdate: result.transaction.creditCard.expirationDate,
            transactionid: result.transaction.id
          })
          .returning('transactionid')
          .then(transactionid => {
            logger.info('[Braintree db] Transaction enregistrée: %s', transactionid);
            res.send(transactionid)
          }).catch((error) => logger.error('[Braintree db] Transaction non enregistrée %s', error));
      } else {
        logger.error('[Braintree] Erreur de transaction: %s', result.message);
        res.sendStatus(500);
      }
    });
  };

gistfile2.txt

Error [ERR_HTTP_HEADERS_SENT]: Cannot set headers after they are sent to the client