Are all files on OwnCloud E2EE weather one has a personal cloud storage account or has an account on a team were files are E2EE for all users that are apart of the same team? E2EE were the server admins cannot see anyones filea, folders, file names, folder names and other metadata?
For audiobooks I go to audiobookstore.com and buy gifts cards using a credit card and I buy the credit cards from Cakepay or Trocador.
https://audiobookstore.com/gift-certificates.aspx