First time flying buddy pass

Hey there! Just wondering as this is my first time flying buddy pass I will be flying out Tuesday and I’m sure I wasn’t charged the 50 dollar fee as they are unsure if I will get the seat.

however I’m wondering if it charges you when the pass is sent out day of, or when I should expect to see it on my statement. Does it charge you even if you were unable to get a flight? Or does it charge you after you land.

Thanks!