Online sales commission entries along with gst

Hello..i am working in the resort.And some of the customers book their rooms through MMT. And later MMT pay to us after deducting their commission. Can someone please help me..how to show that commission entry in tally i.e., in saales voucher or journal voucher? because they charge IGST @ 18% on commission. how will it reflect in GSt?

please help

1st entry you should make as the others .....

Customer A/c Dr.

 To Room Charges/ Hotel Charges ( Whatever your income head )

2nd Entry

MMT A/c Dr.

To Customer A/c 

3rd 

Commission A/c Dr.

 To MMT A/c

4th

Bank/Cash A/c Dr.

To MMT A/c.