Sizing is about risk — how much you lose if the stop is hit. Your broker also needs margin — collateral to hold the position open. They are different numbers, and a trade sized correctly for risk can still be refused for margin.
Why it happens
- Several positions already open, each consuming margin.
- Floating loss on open trades eating free margin before any stop is hit.
- High-margin instruments (indices, metals) alongside forex.
- Leverage lower than you assumed on that account type.
What to change
- Max open positions. This is the practical margin control — cap the book, not just each trade.
- Max positions per symbol, so one instrument cannot dominate.
- Lower risk per trade, which lowers size, which lowers margin.
What not to do
Do not raise leverage to make the error go away. It removes the warning, not the exposure — and the next volatile session collects.
The broker's own message is recorded verbatim in the trade log; if it names a specific margin level, that is the authoritative number.