Why would as 15 affect expenses?

India adopted AS 15 from April 1 2018.  

Check this quarterly statement from PTC

https://www.ptcindia.com/files/investor_relation/Results%20Jun%202018_Final.pdf

If you check 4a Expenses, there is the line for Purchases
which says Purchases (Refer Note 9).

If you go below to Note 9, it refers to AS 15 - revenue from contracts with customers.

Since AS 15 concerns revenue, I do not understand how it affects Expenses/Purchases? Can someone explain this to me?

PTC is a power trading company.