I haven't tested this out but this should be a quick and easy of doing this.

• create a new usegroup
• create a new paid subscription.
  • Users should get added to the new usergroup you just created.
  • subscription length should be set to one day.
• use the ebux paychex system to give users in the new usergroup x points per day.

@reeva, this isn't a good way to do it, as you would have to make a new usergroup for every amount of credits you want to sell.
However, if somebody is willing to pay €50 (or more) for it, I want to do this.

That's not true. If you set it to one day, and make the paycheck pay everyone in that usergroup at 12:00pm every day, then it'd work perfectly. Then you can set different payment amounts: one day for $1.00, two days for $2.00, and so on. Then when the paycheck goes off againt the next day, you're given the amount again.

While writing that out, I realized what you meant. You'd have to pay over a period of time, hmm? Yeah. Not likin that now.