https://travis-ci.org/github/MarcoFalke/btc_nightly/jobs/680655419#L412
"\nSet the transaction fee per kB for this wallet. Overrides the global -paytxfee command line parameter.\n"
                "Can be deactivated by passing 0 as the fee. In that case automatic fee selection will be used by default.\n",
                {
                    {"amount", RPCArg::Type::AMOUNT, RPCArg::Optional::NO, "The transaction fee in " + CURRENCY_UNIT + "/kB"},
                },
                RPCResult{
                    RPCResult::Type::BOOL, "", "Returns true if successful"
                },
                RPCExamples{
                    HelpExampleCli("settxfee", "0.00001")
            + HelpExampleRpc("settxfee", "0.00001")
                },
            }.Check(request);
    LOCK(pwallet->cs_wallet);
    CAmount nAmount = AmountFromValue(request.params[0]);
    CFeeRate tx_fee_rate(nAmount, 1000);
    CFeeRate max_tx_fee_rate(pwallet->m_default_max_tx_fee, 1000);
    if (tx_fee_rate == CFeeRate(0)) {
        
    } else if (tx_fee_rate < pwallet->chain().relayMinFee()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than min relay tx fee (%s)", pwallet->chain().relayMinFee().ToString()));
    } else if (tx_fee_rate < pwallet->m_min_fee) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be less than wallet min fee (%s)", pwallet->m_min_fee.ToString()));
    } else if (tx_fee_rate > max_tx_fee_rate) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("txfee cannot be more than wallet max tx fee (%s)", max_tx_fee_rate.ToString()));
    }
    pwallet->m_pay_tx_fee = tx_fee_rate;
    return true;
}
static UniValue getbalances(const JSONRPCRequest& request)