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O.O stack your sps, around 3000 sps stacked give you one voucher per day, 300 give you 0.1 every day and so on, other way you can buy it for a secondary market, other way you can buy the pack alone for a secondary market for a cheaper price, other way wait around 2 months for the vouchers are no longer requiered to buy packs, you can check my post about packs been cheapers than vouchers for more information: https://www.splintertalk.io/@caimanx/packs-are-cheapers-than-vouchers-and-both-prices-are-falling-down

They're only being sold on the native secondary market found at hive-engine:
https://hive-engine.com/?p=market&t=VOUCHER