ADVANCED RECEIVED UNDER SERVICE TAX.

hi
We have received advanced of rs. 100000 in Feb 2017 and pay the service tax on that amount i'e .18000.(S.Tax.).

and show in our balance sheet as "advanced Received form customer"

Now customer made full and final payment in September 2017 ( 200000)after Service rendered to him.

Total payment received is 300000.

please suggest us what should be invoiced value and GST paid on which amount. and what is the treatment of. advanced Received in feb 2017.