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MQL5 runtime error reference

MQL5 Error 4756: Trade request sending failed

MQL5 error 4756 officially means "Trade request sending failed." OrderSend could not send the request at the terminal runtime layer, or developers use 4756 as a generic label while the actionable server reason is in MqlTradeResult.retcode. Log both GetLastError and MqlTradeResult fields, validate the complete MqlTradeRequest with OrderCheck, and repair the specific request, permission, connection, or server condition shown by those diagnostics. Capture GetLastError immediately around the failing call so an older error is not mistaken for the current failure.

Open MQL5 Coding AgentReview the diagnostic example

Open the Coding Agent and choose MQL5 from the language menu.

Isolate runtime error 4756.mq5
MqlTradeCheckResult check={};
ResetLastError();
bool checked=OrderCheck(request,check);
int check_error=GetLastError();
PrintFormat("checked=%s runtime=%d retcode=%u comment=%s",
            checked ? "true" : "false",check_error,check.retcode,check.comment);
if(!checked) return;

ResetLastError();
bool sent=OrderSend(request,result);
PrintFormat("sent=%s runtime=%d retcode=%u comment=%s",
            sent ? "true" : "false",GetLastError(),
            result.retcode,result.comment);
  • Official meaning: Trade request sending failed
  • Layer: terminal runtime
  • Read with: GetLastError
  • First step: isolate the failing call

Where error 4756 comes from

OrderSend could not send the request at the terminal runtime layer, or developers use 4756 as a generic label while the actionable server reason is in MqlTradeResult.retcode. The numeric value is listed in the official runtime error table, which is separate from MetaEditor compilation errors and trade server return codes.

Reset the last-error state before the suspected call, save its direct return value, and read GetLastError immediately afterward. This produces a causal log instead of a stale code.

Checks that narrow the cause

Preserve the exact parameters and terminal context that produced the failure. Check one precondition at a time before adding retries.

  • Zero-initialize MqlTradeRequest and MqlTradeResult before populating fields.
  • Log action, symbol, order type, volume, price, stops, filling, and expiration.
  • Check terminal and EA trade permissions plus the connection state.
  • Inspect result.retcode for server causes such as 10018 or 10027.

Apply the smallest repair

Log both GetLastError and MqlTradeResult fields, validate the complete MqlTradeRequest with OrderCheck, and repair the specific request, permission, connection, or server condition shown by those diagnostics.

After the repair, test both the expected path and a deliberately invalid input. The second test confirms that the diagnostic branch still exposes failures.

Use a focused diagnostic

This function-body fragment assumes a populated request and initialized result. It records precheck and send results separately; it does not construct a request or enforce a complete risk policy. OrderCheck success cannot guarantee a fill. Test the enclosing execution logic only in a demo environment.

A clean compile or a cleared error code does not prove strategy logic, broker compatibility, backtest quality, or live-trading safety. Reproduce the result in the target MetaTrader 5 terminal and account environment.

Isolate runtime error 4756.mq5
MqlTradeCheckResult check={};
ResetLastError();
bool checked=OrderCheck(request,check);
int check_error=GetLastError();
PrintFormat("checked=%s runtime=%d retcode=%u comment=%s",
            checked ? "true" : "false",check_error,check.retcode,check.comment);
if(!checked) return;

ResetLastError();
bool sent=OrderSend(request,result);
PrintFormat("sent=%s runtime=%d retcode=%u comment=%s",
            sent ? "true" : "false",GetLastError(),
            result.retcode,result.comment);
Where Pineify fits

Repair editable MQL5 source with compiler feedback

Pineify can generate or revise MQL5 source and use MQL5 compilation diagnostics during the coding workflow. Keep the exact error, source location, program type, and intended behavior in the request so the change remains reviewable.

Open MQL5 Coding Agent

Pineify does not run your broker terminal, Strategy Tester, market data, or live orders. Validate the final program in your own MetaTrader 5 environment.

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A practical verification workflow

  1. 1

    Reset the error state

    Call ResetLastError directly before the suspected function so the next code belongs to that operation.

  2. 2

    Record call and inputs

    Save the function return value, every input, and GetLastError. Confirm that the captured runtime code is 4756.

  3. 3

    Validate the preconditions

    Zero-initialize MqlTradeRequest and MqlTradeResult before populating fields. Log action, symbol, order type, volume, price, stops, filling, and expiration. Check terminal and EA trade permissions plus the connection state. Inspect result.retcode for server causes such as 10018 or 10027.

  4. 4

    Retest in the target terminal

    Compile the changed source, repeat the failing operation, and test the surrounding EA or indicator behavior in MetaTrader 5.

Frequently asked questions

What does MQL5 error 4756 mean?

The official runtime error table defines 4756 as "Trade request sending failed."

Is error 4756 a compiler error?

No in this context. It is a terminal runtime code. Compiler diagnostics and MqlTradeResult.retcode values use separate code tables.

Why should I call ResetLastError first?

The terminal stores the last runtime error. Resetting it before the suspected call makes the following GetLastError value easier to attribute to that call.

Check the linked official references for the relevant diagnostic. Compile and test the final source in the MetaTrader 5 build, broker, symbol, and account environment you plan to use.

Continue with reviewable MQL5 source

Provide the exact diagnostic and intended behavior, inspect the generated change, compile it, and verify it in your MT5 test environment.

Open MQL5 Coding Agent