High-Frequency Trading (HFT) isn't allowed on any account. Automation is allowed as long as it doesn't trade in an HFT style.
What counts as HFT
Systems that place, modify or cancel orders in milliseconds or at extremely high speed.
Executing hundreds or thousands of trades per second or minute.
Order spamming, or repeatedly placing and canceling orders at high speed.
Latency-based strategies that exploit price differences in milliseconds or microseconds.
Excessive trade volume over very short periods.
Why it's prohibited
HFT creates unfair advantages and can overload trading systems. Keeping it out gives every trader the same conditions.
Consequences
Trade frequency, volume and execution patterns are monitored. An account suspected of HFT is suspended pending review. If a prohibited strategy is confirmed, all accounts involved are closed and unpaid profits on them are forfeited. Serious or repeat violations lead to a full ban. Payouts approved before the finding are honored.