Hey everyone

What is the word to describe the following:
"A user pays a set price to their mobile phone operator to send an SMS message. But in fact, there's a service provider in the middle that does the work so the operator has to give back a certain part of the money paid by the user back to the service provider".
Is "payout" the correct word to describe the operation of giving back part of a sum of money? Is there another word that would be more appropriate?
Thanks for any help as always.