https://travis-ci.org/github/bitcoin/bitcoin/jobs/679885530#L8791
warnings.push_back(AmountHighWarn("-paytxfee") + Untranslated(" ") +
                               _("This is the transaction fee you will pay if you send a transaction."));
        }
        walletInstance->m_pay_tx_fee = CFeeRate(nFeePerK, 1000);
        if (walletInstance->m_pay_tx_fee < chain.relayMinFee()) {
            error = strprintf(_("Invalid amount for -paytxfee=<amount>: '%s' (must be at least %s)"),
                gArgs.GetArg("-paytxfee", ""), chain.relayMinFee().ToString());
            return nullptr;
        }
    }
    if (gArgs.IsArgSet("-maxtxfee")) {
        CAmount nMaxFee = 0;
        if (!ParseMoney(gArgs.GetArg("-maxtxfee", ""), nMaxFee)) {
            error = AmountErrMsg("maxtxfee", gArgs.GetArg("-maxtxfee", ""));
            return nullptr;
        }
        if (nMaxFee > HIGH_MAX_TX_FEE) {
            warnings.push_back(_("-maxtxfee is set very high! Fees this large could be paid on a single transaction."));
        }
        if (CFeeRate(nMaxFee, 1000) < chain.relayMinFee()) {
            error = strprintf(_("Invalid amount for -maxtxfee=<amount>: '%s' (must be at least the minrelay fee of %s to prevent stuck transactions)"),
                gArgs.GetArg("-maxtxfee", ""), chain.relayMinFee().ToString());
            return nullptr;
        }
        walletInstance->m_default_max_tx_fee = nMaxFee;
    }
    if (chain.relayMinFee().GetFeePerK() > HIGH_TX_FEE_PER_KB) {
        warnings.push_back(AmountHighWarn("-minrelaytxfee") + Untranslated(" ") +
                           _("The wallet will avoid paying less than the minimum relay fee."));
    }