wallet: rpc: Improve error message for low feerates. #34640

1. 
   davidgumberg commented at 10:38 pm on February 20, 2026: contributor

   Giving the user a hint about what action to take when they encounter an error related to a feerate that is below the minimum. I encountered this myself not knowing about -mintxfee and the manpage was slightly less than clear,

   0       -mintxfee=<amt>
   1
   2              Fee rates (in BTC/kvB) smaller than this are considered zero fee for  transaction  creation
   3              (default: 0.00001)
   

2. wallet: rpc: Improve error message for low feerates. b77555c8fb
3. DrahtBot added the label Wallet on Feb 20, 2026
4. 
   DrahtBot commented at 10:39 pm on February 20, 2026: contributor

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   Concept ACK	rkrux, musaHaruna

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5. in src/wallet/rpc/spend.cpp:1438 in b77555c8fb

   1434@@ -1435,7 +1435,18 @@ RPCHelpMan sendall()
   1435             // Do not, ever, assume that it's fine to change the fee rate if the user has explicitly
   1436             // provided one
   1437             if (coin_control.m_feerate && fee_rate > *coin_control.m_feerate) {
   1438-                throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Fee rate (%s) is lower than the minimum fee rate setting (%s)", coin_control.m_feerate->ToString(FeeRateFormat::SAT_VB), fee_rate.ToString(FeeRateFormat::SAT_VB)));
   1439+                const auto f = FeeRateFormat::SAT_VB;
   

   ---

   ---

   

   rkrux commented at 12:22 pm on February 25, 2026:

   Sure its usage is limited and bounded but calling it just f doesn’t help the reader much.
6. in src/wallet/rpc/spend.cpp:1447 in b77555c8fb

   1443+                if (fee_calc_out.reason == FeeReason::REQUIRED) {
   1444+                    msg += strprintf("\nConsider modifying %s (%s) or %s (%s).",
   1445+                        "-mintxfee",
   1446+                        pwallet->m_min_fee.ToString(f),
   1447+                        "-minrelaytxfee",
   1448+                        pwallet->chain().relayMinFee().ToString(f));
   

   ---

   ---

   

   rkrux commented at 12:26 pm on February 25, 2026:

   I don’t see a strong reason to add placeholders for hardcoded values. The following diff for succinctness?

    0--- a/src/wallet/rpc/spend.cpp
    1+++ b/src/wallet/rpc/spend.cpp
    2@@ -1440,10 +1440,8 @@ RPCHelpMan sendall()
    3                     coin_control.m_feerate->ToString(f),
    4                     fee_rate.ToString(f))};
    5                 if (fee_calc_out.reason == FeeReason::REQUIRED) {
    6-                    msg += strprintf("\nConsider modifying %s (%s) or %s (%s).",
    7-                        "-mintxfee",
    8+                    msg += strprintf("\nConsider modifying -mintxfee (%s) or -minrelaytxfee (%s).",
    9                         pwallet->m_min_fee.ToString(f),
   10-                        "-minrelaytxfee",
   11                         pwallet->chain().relayMinFee().ToString(f));
   12                 }
   

7. 
   rkrux commented at 12:33 pm on February 25, 2026: contributor

   Concept ACK for the intent to add an actionable message in case of this error.
8. 
   musaHaruna commented at 10:11 am on February 26, 2026: contributor

   Concept ACK on improving error message for low feerates

   Sure its usage is limited and bounded but calling it just f doesn’t help the reader much.

   Also agree with this comment. I think naming the variable format or fee_rate_format makes it more readable.

Contributors
davidgumberg DrahtBot rkrux musaHaruna

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Wallet