The question is not much clear. What I understood is, you are receiving commission from a foreign principal in a foreign currency. So, this is an export of service. Subject to other conditions, it is a zero rated supply.
Hence, you have 2 options:
1. Export while paying IGST and claim back the refund.
2. Export under bond/LuT without payment of GST.
Going with Option 1,
# You have to pay IGST @ 18%.
# This is under normal charge.
# In GSTR 1, enter this detail under Export.
# Claim refund of such IGST paid in Form GST RFD 01.
# FIRC copies are mandatory for each such foreign remittance.