MT5 invalid volume error

Causes, most likely first

1. The lot size is below the symbol minimum

Most brokers set a 0.01 minimum, but some use 0.10 on metals and a few use higher minimums on specific account types. A position-sizing calculation returning 0.004 lots must be rounded up to the minimum or skipped — and rounding up means the trade risks more than you configured.

2. The lot size is not a multiple of the volume step

Volumes must align to the symbol's step, usually 0.01. A calculated 0.037 lots is invalid and must be rounded to 0.03 or 0.04. Read the step from Market Watch → Specification, since a few brokers use 0.1 on gold.

3. The lot size exceeds the maximum per order

Symbols carry a maximum volume per order and often a maximum total exposure. Large accounts hit this and need positions split across multiple orders.

4. The account has a total position limit

Separate from the per-order maximum, some brokers cap the aggregate volume open on one symbol. The rejection looks identical, but it appears only once several positions are already open.

Why this happens

Volume quantisation is more consequential than it appears, because it puts a floor under risk. If your sizing formula wants 0.004 lots and the minimum is 0.01, your real risk is two and a half times what you configured — and nothing in the platform warns you.

This is the specific reason a "minimum balance" for any gold bot cannot be stated as a single number. The floor interacts with stop distance: a tighter stop lowers the balance at which the minimum stops binding, a wider one raises it.

The lot size calculator shows both the calculated size and whether the broker minimum has overridden it, which is the warning most calculators omit.