If you have 0 pips available and no open trades, you have failed the level. If you have 0 pips available and one or more open trades, you cannot open a new trade until you either close an existing position or reduce the SL distance of an existing trade.
Example 1:
You have 20 pips available. Opening a EUR/USD trade with a 10-pip SL reduces your available pips to 10. Those 10 pips are locked into the EUR/USD trade, leaving 10 pips to risk on other trades.
The maximum SL you can place on the next trade is 10 pips. Adjusting the SL on your EUR/USD trade can increase or decrease your available pips:
Reduce the SL from 10 pips to 5 pips, increasing your available pips to 15.
Increase the SL from 10 pips to 15 pips, decreasing your available pips to 5.
Example 2:
If you have 0 pips available and an open GBP/USD trade with a 20-pip SL, you cannot open any new trades until you make adjustments:
Reduce the SL on your GBP/USD trade from 20 pips to 10 pips, increasing your available pips to 10, allowing you to open a new trade with a 10-pip SL or keep those 10 pips available for future trades.