suspected new trick by grab, or maybe just a system glitch.

First , i booked a ride home with code <4mph> provided by grab.
i waited for a long time, driver never show up. So i check the app again, it says that the ride has completed and I have paid rm5 , which did not bother me as it led me to an unlocked code <50mph> (rm5 discount)

So i booked a ride again with the code <50mph> (trip was rm9 ,discounted rm5 = rm4 )
,but when i arrived , the final amount shown on driver's phone was rm9 . ironically , driver's phone also showed that i have entered a promo for the ride.

the driver was confused too at the moment and he even apologised to me.

what even