Can OTA take commission on GST paid by the customer to hotel??

Here i am attaching a booking voucher which shows all the price breakups..

In the below voucher we are paying 18% commission for 191.88 INR (paid by customer to us as GST)  to OTA .

Is that legit under law?? Does OTAs have permission to take commssion for the GST paid by customer to hotel ??