Unsupported filling mode: the MT5 rejection that confuses new users

[Amanhasnoname]

An MT5 order can fail with a message about unsupported filling mode, and the cause is a mismatch between what the code requests and what the symbol allows. Symbols support combinations of fill-or-kill, immediate-or-cancel, and return. Each broker and symbol can differ.

A script written on one broker may fail on another because the default fill type is not permitted. Even within a broker, forex pairs and indices can have different rules.

The fix is querying the symbol's filling mode flags before sending, and picking an allowed type. Many libraries do it automatically, but homemade code often hardcodes one choice.

Beyond avoiding errors, the fill type affects behavior. Fill-or-kill rejects when full size is unavailable. Immediate-or-cancel takes what is available. Return allows partial fills to rest as pending orders, which is a nasty surprise for a scalper who expects a clean exit.

Check which mode the EA uses and confirm it matches the intent for each order type.

Which filling mode does the strategy use, and was that a conscious choice?