GST Calculation

Hi,

We are a travel agency, We are currently setting up zoho books for us, having issues in gst, When purchasing airticket, we recieve our commission as discount from our supplier, and on the commission gst is charged gst @18% by our supplier and we have to charge our customer 18% for the service charges charged by us. How to setup this zoho books.

Thanks
Regards
Bharani Muthuvel
98403 95760