MQL5 error 4756: trade request sending failed (fix)

What it means

OrderSend(), or a CTrade method that calls it, returned false. That's all 4756 tells you: the request was refused. The reason is a second number, the trade server return code in MqlTradeResult.retcode. Code that only prints GetLastError() never sees it.

Usual causes

4756 comes with a retcode. The ones EAs meet most:

• 10016, invalid stops: stop-loss or take-profit too close, or on the wrong side.
• 10030, unsupported filling mode: a filling policy the symbol doesn't accept.
• 10019, not enough money and 10014, invalid volume: the volume.
• 10015, invalid price and 10004, requote: the price.
• 10018, market closed, 10017, trade disabled and 10027, autotrading disabled: trading isn't possible right now.
• 10013 (TRADE_RETCODE_INVALID, "Invalid request"): a field the action needs is missing or doesn't fit it. Compare your request with the fields MqlTradeRequest lists for that action.

How to detect it

• With raw OrderSend(req, res): print res.retcode and res.comment (by default the broker fills the comment with the retcode's description).
• With CTrade: trade.ResultRetcode(), trade.ResultRetcodeDescription() and trade.ResultComment(). CTrade also prints the failed request in the Experts tab.
• Call ResetLastError() before the trade call, so the GetLastError() you read belongs to it.

Broken code

This script compiles, and tries to open a minimum-volume buy when run. It fails, and the log only says "error 4756".

void OnStart()
  {
   MqlTradeRequest req = {};
   MqlTradeResult  res = {};
   req.action       = TRADE_ACTION_DEAL;
   req.symbol       = _Symbol;
   req.volume       = SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_MIN);
   req.type         = ORDER_TYPE_BUY;
   req.price        = SymbolInfoDouble(_Symbol, SYMBOL_ASK);
   req.sl           = req.price;            // a stop at the entry price: refused
   req.type_filling = ORDER_FILLING_IOC;
   if(!OrderSend(req, res))
      Print("OrderSend failed, error ", GetLastError());   // prints 4756, never the reason
  }

Fixed code

The same program with the check that prevents the error. It compiles in MetaEditor with 0 errors and 0 warnings.

void OnStart()
  {
   MqlTick tick;
   if(!SymbolInfoTick(_Symbol, tick))
      return;
   MqlTradeRequest req = {};
   MqlTradeResult  res = {};
   req.action       = TRADE_ACTION_DEAL;
   req.symbol       = _Symbol;
   req.volume       = SymbolInfoDouble(_Symbol, SYMBOL_VOLUME_MIN);
   req.type         = ORDER_TYPE_BUY;
   req.price        = tick.ask;
   req.sl           = NormalizeDouble(tick.bid - 300 * _Point, _Digits);
   req.deviation    = 10;
   req.type_filling = ORDER_FILLING_IOC;

   ResetLastError();
   if(!OrderSend(req, res))
     {
      // 4756 says it failed; the retcode says why
      PrintFormat("OrderSend failed: error %d, retcode %u (%s), bid %s ask %s sl %s, stops level %d",
                  GetLastError(), res.retcode, res.comment,
                  DoubleToString(tick.bid, _Digits), DoubleToString(tick.ask, _Digits), DoubleToString(req.sl, _Digits),
                  (int)SymbolInfoInteger(_Symbol, SYMBOL_TRADE_STOPS_LEVEL));
      return;
     }
   if(res.retcode != TRADE_RETCODE_DONE && res.retcode != TRADE_RETCODE_PLACED)
      PrintFormat("Accepted but not done: retcode %u (%s)", res.retcode, res.comment);
  }

Why the fix works

The fixed script logs the retcode and the broker's comment along with 4756, plus the prices and the stops level, which is everything you need to diagnose the failure from one line of the journal. The stop is also measured from the Bid and placed 300 points away, instead of at the entry price.

Note the last check: OrderSend() returning true only means the request passed the basic checks and was accepted. The retcode still says what happened: 10009 (TRADE_RETCODE_DONE) for a completed request, 10008 (TRADE_RETCODE_PLACED) for a placed order, 10010 when only part of the volume was filled. The fixed script still uses IOC as its filling policy; choose it from the symbol's flags as shown for error 10030.

Questions

The programs on this page are minimal examples written to show the error and its fix, not trading systems. Some of them send orders when they run: try them on a demo account. Trading involves substantial risk of loss and is not suitable for every investor. Edgoro is a software tool, not a broker or financial adviser: nothing it produces is investment advice, and past or backtested performance does not guarantee future results.