This means that you've run out of daytrading buying power, which is calculated as part of the Day Trade Margin Call (DTMC) Protection. The calculation is as follows:

daytrading_buying_power = 4 * (last_equity - last_maintenance_margin)

All these values can be obtained from your account info.

For example, if your last_maintenance_margin was greater than your last_equity, then you'll have a daytrading_buying_power of zero. Both of these are calculated at end of the last trading day, so closing overnight positions will not add to your daytrading buying power.

Please visit this webpage to see more information on what is maintenance margin.

Alpaca uses the following table to calculate the overnight maintenance margin applied to each security held in an account:

Maintenance margin
Margin & Short Selling
Margin and Short Selling # In order to trade on margin or sell short, you must have $2,000 or more account equity. Accounts with less than $2,000 will not have access to these features and will be restricted to 1x buying power. This do not apply to Crypto Trading. Margin Trading for Crypto is not a…