How will Apple get the money for my repair?

I want to send Apple my iPhone so they can repair it. They send me a box and I put my phone in it and send it back to the nearest Apple store and they send it back. My question is how will Apple get the money I owe them them for the repare? Do I send if with the box they sent me? Do I have to do it online with a credit card? Do I have to go to the Apple store I send my phone to and pay it there?

Credit card… You can pay online

Okay.