GTA Reverse Charge

GTA service is exempted from GST only when the follwoing conditions are satisfied:

a)goods, where gross amount charged for the transportation of goods on a consignment transported in a single carriage does not exceed one thousand five hundred rupees; and
b) goods, where gross amount charged for transportation of all such goods for a single consignee does not exceed rupees seven hundred fifty;

So in your case even if your GTA charges are less than Rs.750, but overall consignment value for shipment may exceed Rs.1500. In that case you need to discharge GST on that.