An inverted fair value gap (FVG) occurs when candles start closing below a bullish FVG or above a bearish FVG and in this case, support FVGs become resistances and vice versa. This is a smart money concept introduced by ICT. While we a number of have indicators for FVGs, we don't have any for inversion FVGs. This indicator is just for that - it shows FVGs only after they're inverted.
The meat of it comes from being able to plot HTF inverted FVGs in LTF. In the above BTC chart, you can see M15 inverted FVGs plotted on M1 chart and you can see price respecting them. Mitigations can also be shown as lines (as you can see in the chart).
You can also setup alerts for formation and mitigation of such inversion FVGs.