RCM OF Freight

We sale goods on trading, We send goods on FOR basis and we charge GST On freight same rate as goods, so my question is we require to pay RCM on freight on which we collect gst @ 18% and paid to department.

we have 2 data
1. freight on which we collect 18% gst
2. freight on which only exp has booked
no gst collect from buyer

on which we require to pay rcm

if we not pay rcm on 1 point then any case law available for remedy