GST on Advance Received in August 2017

Deepak Kashyap (assistant Accountant) (52 Points)

31 January 2018  
We received Advance form Party in August 2017 I issued Receipt voucher for this after doing GST @ 18 treatment. Now That Party is asking for refund back that amount.I have to issue refund voucher or same amount with reversal of GST @ 18.Refund voucher ?