Hello mam

First of all hats of to you.you give a lot of valuable information about GST. Awesome!!!!!!!!!!

mam, I am an eCommerce seller and I sell in the category of 5 %  my question is how to get refund our excess GST from the govt.  in Electronic Credit Ledger. is it possible for eg: I purchase 1 product at 100/- GST paid 5 Rs and I sell at 300/- my tax liability is 10 Rs but amazon charge me 18 % GST on commission and courier which is around 27 Rs but my liability is 10 the how do I get a refund of that 17 rs.
 
this is my question
 
regards
sachit