Why your EA says “Unsupported filling mode”

2 October 2026 · Soft Trade Enterprises · All guides

The symptom

You move a working EA to a new broker, or your broker changes something server-side. Suddenly no trades open. The Experts log shows:

OrderSend failed. Retcode: 10030  // TRADE_RETCODE_INVALID_FILL

Nothing is wrong with your strategy. The EA is asking the server to fill the order in a way that this particular broker, on this particular symbol, does not accept.

The three filling modes

Mode	Meaning	If it cannot be fully filled
ORDER_FILLING_FOK	Fill or Kill	The whole order is cancelled
ORDER_FILLING_IOC	Immediate or Cancel	Fills what it can, cancels the rest
ORDER_FILLING_RETURN	Return	Fills what it can, the remainder stays as a pending order

Each broker decides which modes it supports, per symbol. It is not an account-level setting and it is not something you can assume.

The mistake

Most EAs that break this way have the mode hard-coded, usually because it worked during development:

request.type_filling = ORDER_FILLING_FOK;  // works here, fails there

That line is the whole bug. It is correct on one broker and wrong on the next.

The fix — ask the symbol

The terminal already knows which modes the symbol allows. Read it instead of guessing:

ENUM_ORDER_TYPE_FILLING PickFilling(const string symbol)
{
   int allowed = (int)SymbolInfoInteger(symbol, SYMBOL_FILLING_MODE);

   if((allowed & SYMBOL_FILLING_FOK) != 0) return ORDER_FILLING_FOK;
   if((allowed & SYMBOL_FILLING_IOC) != 0) return ORDER_FILLING_IOC;

   // Neither flag set: the symbol uses RETURN (market execution)
   return ORDER_FILLING_RETURN;
}

Two details that catch people out. SYMBOL_FILLING_MODE is a bit mask, so test it with &, never with ==. And ORDER_FILLING_RETURN has no flag of its own — when neither FOK nor IOC is set, RETURN is what the symbol uses.

Pending orders follow a different rule

Pending orders (limit and stop) generally use ORDER_FILLING_RETURN regardless of what the symbol reports for market orders. If your EA places pending orders, handle them separately rather than reusing the market-order mode.

Check this at startup, not at the first trade

Resolve the filling mode once in OnInit() and refuse to start if nothing workable is available. Finding out at 2am, on the first signal of the week, is the expensive version.

int OnInit()
{
   if(!SymbolSelect(_Symbol, true))
   {
      Print("Symbol not available: ", _Symbol);
      return INIT_FAILED;
   }
   g_filling = PickFilling(_Symbol);
   Print("Filling mode resolved to: ", EnumToString(g_filling));
   return INIT_SUCCEEDED;
}

Related retcodes worth knowing

Retcode	Constant	Usual cause
10030	TRADE_RETCODE_INVALID_FILL	Filling mode not supported
10016	TRADE_RETCODE_INVALID_STOPS	Stop closer than the broker's minimum
10014	TRADE_RETCODE_INVALID_VOLUME	Lot below minimum, above maximum, or off the step
10019	TRADE_RETCODE_NO_MONEY	Insufficient free margin
10027	TRADE_RETCODE_CLIENT_DISABLES_AT	Algo Trading button is off

Always print the retcode and the comment from the result structure. "OrderSend failed" on its own tells nobody anything; the retcode tells you exactly which of these it was.