Daytrading_buying_power ? how to calculate it?

I am a little confused by daytrading_buying_power and buying power. My account information is as below. Why the buying_power is 53617.21 but daytrading_buying_power is only 10928.028 ? How to calculate daytrading_buying_power ?

‘buying_power’: ‘53617.21’, ‘regt_buying_power’: ‘53617.21’, ‘daytrading_buying_power’: ‘10928.028’, ‘cash’: ‘-59794.96’, ‘portfolio_value’: ‘113412.17’, ‘pattern_day_trader’: False, ‘trading_blocked’: False, ‘transfers_blocked’: False, ‘account_blocked’: False, ‘created_at’: ‘2020-04-10T05:51:07.345974Z’, ‘trade_suspended_by_user’: False, ‘multiplier’: '4

When submit an order > daytrading_bying_power, e,g, #15000, it is rejected and show no sufficient daytrading buying power. but the buying power is still > 15000, how to understand that ?

daytrading_buying_power = 4 * (last_equity - last_maintenance_margin)

Seems not right ?

If based on my last pull of the account. Equity = 120921.79, last_maintainance_margin = 92417.982, daytrading_buying_power = 114015.23, if calculated by daytrading_buying_power = 4 * (last_equity - last_maintenance_margin). But the account shows only 17601.292

‘buying_power’: ‘84078.07’, ‘regt_buying_power’: ‘84078.07’, ‘daytrading_buying_power’: ‘17601.292’, ‘cash’: ‘-5334’, ‘portfolio_value’: ‘120921.79’, ‘pattern_day_trader’: False, ‘trading_blocked’: False, ‘transfers_blocked’: False, ‘account_blocked’: False, ‘created_at’: ‘2020-04-10T05:51:07.345974Z’, ‘trade_suspended_by_user’: False, ‘multiplier’: ‘4’, ‘shorting_enabled’: False, ‘equity’: ‘120921.79’, ‘last_equity’: ‘122722.28’, ‘long_market_value’: ‘126255.79’, ‘short_market_value’: ‘0’, ‘initial_margin’: ‘78882.755’, ‘maintenance_margin’: ‘83404.833’, ‘last_maintenance_margin’: ‘92417.982’, ‘sma’: ‘0’, ‘daytrade_count’: 24}