Erro order_send failed

That would be an invalid volume error.

10014

TRADE_RETCODE_INVALID_VOLUME

Invalid volume in the request

What are the contract specifications for that symbol regarding volume?

Is you code checking them?

SYMBOL_VOLUME_MIN	Minimal volume for a deal	double
SYMBOL_VOLUME_MAX	Maximal volume for a deal	double
SYMBOL_VOLUME_STEP	Minimal volume change step for deal execution	double
SYMBOL_VOLUME_LIMIT	Maximum allowed aggregate volume of an open position and pending orders in one direction (buy or sell) for the symbol. For example, with the limitation of 5 lots, you can have an open buy position with the volume of 5 lots and place a pending order Sell Limit with the volume of 5 lots. But in this case you cannot place a Buy Limit pending order (since the total volume in one direction will exceed the limitation) or place Sell Limit with the volume more than 5 lots.	double

use my function below, to Validade the LOT Size and Step. It verifies the LOT Size and Step, according to Symbol Specifications, the and rounds it to the correct Volume and Step 

CSymbolInfo             ativo;


//Rounds and ajust the LOT and STEP as defined on its specifications

double ArredondaLoteComStep(double lote)
{

    double lote_arredondado = 0;
    double lot_step   =  ativo.LotsStep();
    double lot_max    =  ativo.LotsMax();
    double lot_min    =  ativo.LotsMin();


    if (lote > lot_max) lote = lot_max;     
    if (lote < lot_min) lote = lot_min;     

// Round it according to its specifications.
//
    lote_arredondado =  ( MathFloor( (lote + (0.5 * lot_step)) / lot_step ) * lot_step );


    if (lote_arredondado > lot_max) lote_arredondado = lot_max;     
    if (lote_arredondado < lot_min) lote_arredondado = lot_min;     


    lote_arredondado = NormalizeDouble(lote_arredondado, 2);

    return(lote_arredondado);

}