My suggestion is to make it real simple:
- Do not touch a players premium days at all. They are on the account and remain there.
- Allow every account to buy premium days and specify a target character name (and credit it to the account which holds that character instead of the player's own account).
- I can easily specify the amount of days
- I know the exact costs
- I can understand the system.
- Less space for error (like accidentially donating 2 years of premium)
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