NIL GST for Other Transport Support Services

Dear Friends,

One of our customer is asking us to provide Zero GST Invoice, we are not GTA so, we will not able to show GST under RCM in the Invoice. In this case how so we manage the customer requirements as well how we show this transactions in the GSTR1 & 3B. Showing NIL Returns isn't fair because this is continuing businesses for long term.
Monthly turnover is about 5 Lakhs .
please assist me accordingly.