I paid it when I applied for ARC without it being requested. Even though i I didn't know the outcome then but i still paid it.
But usually when you are approved, they will request the payment, but if you are refused, they will not request. That's what the officer told mme during my interview.
Usually there's no interview but in rare cases and they request the payment after the interview once they have are satisfied that you will be approved.
It's a hard process, been in it for a year until i got approved.