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MQL4 ERR_INVALID_TRADE_VOLUME

MQL4 error 131 invalid trade volume: normalize lots

MQL4 error 131 invalid trade volume maps to ERR_INVALID_TRADE_VOLUME: invalid trade volume. The requested lots violate the symbol minimum, maximum, step, or another broker volume rule. For API calls, check the return value and capture GetLastError after a documented failure. Critical runtime errors require preventive guards and inspection of the terminal log.

Open MQL4 Coding AgentReview the code example

Open the Coding Agent, then choose MQL4 from the language menu.

TradeVolumeDiagnostic.mq4MQL4
#property strict
#property script_show_inputs

input double Lots = 0.10;
input int Slippage = 3;

void OnStart()
  {
   if(!IsTradeAllowed())
     {
      Print("Trading is not currently allowed or the trade context is busy.");
      return;
     }

   RefreshRates();
   double price = NormalizeDouble(Ask, Digits);
   ResetLastError();
   int ticket = OrderSend(Symbol(), OP_BUY, Lots, price, Slippage,
                          0, 0, "diagnostic", 0, 0, clrNONE);

   if(ticket >= 0)
     {
      Print("Order opened. Ticket ", ticket);
      return;
     }

   int error_code = GetLastError();
   Print("OrderSend failed. error=", error_code,
         " symbol=", Symbol(), " lots=", DoubleToString(Lots, 2),
         " ask=", DoubleToString(price, Digits));
  }
  • Official meaning: invalid trade volume
  • Check API results or the runtime failure log
  • Capture relevant inputs and error context
  • Retry only when the condition can change

What MQL4 error 131 means

The official MQL4 runtime table names error 131 ERR_INVALID_TRADE_VOLUME and defines it as “invalid trade volume.” The requested lots violate the symbol minimum, maximum, step, or another broker volume rule.

An error-state value is supporting context, not proof that a call failed or a diagnosis of the whole EA. For noncritical API failures, read the return value and then GetLastError, which resets _LastError. Critical errors such as zero division terminate execution, so code after the failing expression cannot serve as a recovery handler.

Check these conditions before editing the strategy

Start with the inputs and external state that existed at the failure point. A later log entry or a successful call can overwrite the useful context.

  • Lots are below MODE_MINLOT or above MODE_MAXLOT
  • Lots do not align with MODE_LOTSTEP
  • Floating-point rounding produces an unsupported volume
  • The EA applies one symbol’s lot rules to another symbol

Fix the cause, then choose a retry policy

Recalculate the volume once from current symbol properties. Do not repeatedly resend the same invalid lots or round upward beyond the risk budget.

Keep the original trading and risk rules intact. A workaround that widens stops, increases volume, changes an account setting, or ignores a failed return value can hide the symptom while changing the system.

CheckAction
Lots are below MODE_MINLOT or above MODE_MAXLOTRound down within the risk budget, then reject values below the broker minimum or above the maximum; do not increase volume to force acceptance.
Lots do not align with MODE_LOTSTEPRound volume down to the current symbol lot step.
Floating-point rounding produces an unsupported volumeNormalize the result to the precision implied by the lot step.
The EA applies one symbol’s lot rules to another symbolRead min, max, and step for the order symbol at the decision point.

Review the complete example

The script does not normalize lots; it logs Lots to two decimal places, which can hide a finer broker step. Preserve enough precision in diagnostics and validate min/max/step before any demo order. The request itself has no SL/TP.

This script can submit one market buy with no SL or TP. It omits volume, margin, quote-freshness, and duplicate-order controls. Add the required controls and use only a demo account before evaluating this diagnostic.

TradeVolumeDiagnostic.mq4MQL4
#property strict
#property script_show_inputs

input double Lots = 0.10;
input int Slippage = 3;

void OnStart()
  {
   if(!IsTradeAllowed())
     {
      Print("Trading is not currently allowed or the trade context is busy.");
      return;
     }

   RefreshRates();
   double price = NormalizeDouble(Ask, Digits);
   ResetLastError();
   int ticket = OrderSend(Symbol(), OP_BUY, Lots, price, Slippage,
                          0, 0, "diagnostic", 0, 0, clrNONE);

   if(ticket >= 0)
     {
      Print("Order opened. Ticket ", ticket);
      return;
     }

   int error_code = GetLastError();
   Print("OrderSend failed. error=", error_code,
         " symbol=", Symbol(), " lots=", DoubleToString(Lots, 2),
         " ask=", DoubleToString(price, Digits));
  }
Where Pineify fits

Move from the rule to editable MQL4 source

Pineify can generate or revise one self-contained .mq4 file with MQL4-specific reference context. Its independent static checker returns MetaEditor diagnostics so you can repair source issues before testing in your own MT4 environment.

Open MQL4 Coding Agent

Static diagnostics do not prove runtime behavior, backtest results, broker compatibility, or live-trading safety.

Pineify MQL4 Coding Agent with MQL4 selected and an editable MetaTrader 4 code artifact

A practical workflow

  1. 1

    Locate the failed operation

    Check the API result, or the terminal log and source location for a critical runtime failure.

  2. 2

    Capture the error once

    For a recoverable API failure, capture GetLastError immediately. For a terminated program, preserve the terminal log. Record error 131 and the inputs relevant to the failed operation.

  3. 3

    Correct the triggering condition

    Round down within the risk budget, then reject values below the broker minimum or above the maximum; do not increase volume to force acceptance.

  4. 4

    Retest in the target environment

    Compile the revised source, then test with the same MT4 build, broker, symbol, account permissions, and market state.

Frequently asked questions

What does MQL4 error 131 invalid trade volume mean?

ERR_INVALID_TRADE_VOLUME means invalid trade volume. Use the API result or critical runtime log, together with the relevant inputs, to identify the failed operation.

What usually causes MQL4 error 131?

Lots are below MODE_MINLOT or above MODE_MAXLOT. Lots do not align with MODE_LOTSTEP. Floating-point rounding produces an unsupported volume. The EA applies one symbol’s lot rules to another symbol.

Should an EA retry after error 131?

Recalculate the volume once from current symbol properties. Do not repeatedly resend the same invalid lots or round upward beyond the risk budget.

Why should GetLastError be called immediately?

For a noncritical API failure it reports the current _LastError value and resets it. A delayed read may describe another call. It cannot recover execution after a critical error has terminated the program.

Can Pineify fix MQL4 error 131?

Pineify can revise a self-contained .mq4 file, add validation and error logging, and return static MetaEditor diagnostics. It cannot prove broker acceptance, account permissions, market availability, or live execution.

Compile and test the final source in the MetaTrader 4 build, broker, symbol, and account environment you plan to use.

Continue with one reviewable MQL4 file

Define the requirement, inspect the generated source, repair diagnostics, and test the behavior in your own MT4 environment.

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