Placing trades that behave, and reading what came back.
Market closed, invalid volume, invalid stops, no margin, wrong symbol: five reasons a broker refuses a valid MT5 order, and how to read and prevent each.
A market order trades now; a pending order waits at the broker for your price. How each behaves in an MT5 API, with one example and a comparison table.
Why a retry or a double click can open two MT5 positions, and how one request identifier — an idempotency key — makes every order safe to send again.
Test an MT5 trading API safely: connect a broker demo account, read from it, place a small demo order and check the result. A test key alone is no sandbox.