The context of the following conversation is As a responsible parent, Alex bought Carson's phone for him and didn't charge him.:
Alex says Here I'll get that..
The friend responds Why did you just do that?.
Alex responds I wanted to do something nice for you. So you don't have to pay me back..
The friend responds No, I'll pay you every cent back..
Alex responds That defeats my purpose.  I wanted to buy you something, so no you are not paying me back..
The friend responds Okay. Well thank you..