"The warning informs the user that to unlock their system, they would have to pay a fine using a voucher from an anonymous prepaid cash service such as Ukash or Paysafecard.

[...]

By August 2012, a new variant of Reveton began to spread in the United States, claiming to require the payment of a $200 fine to the FBI using a MoneyPak card.

[...]

Rather surprisingly, Fusob suggests using iTunes gift cards for payment." https://en.wikipedia.org/wiki/Ransomware

Apparently at least Ukash, Paysafecard, MoneyPak card, and iTunes gift cards have all been used.