GST on 'Commision on Sale'

md sajruddin khan (full details of gst and hsn code)   (233 Points)

23 November 2018  
Dear Sir/Mam
we working as a CFA and earn Commission on sale but my co. is telling that I will no Issue Credit note and You have to Issue a Tax invoice/Commission Invoice with (hsn/sac no. 9961) and gst 18% Then I will pay you.
so my Question is
1. how we treat this Commision invoice a/c
2. And how we file Gstr this

Kindly Advise me