Voucher

A voucher is a bond of the redeemable transaction type which is worth a certain monetary value and which may be spent only for specific reasons or on specific goods. Examples include (but are not limited to) housing, travel, and food vouchers. The term voucher is also a synonym for receipt and is often used to refer to receipts used as evidence of, for example, the declaration that a service has been performed or that an expenditure has been made.

Battlefield Hardline
"Redeem vouchers in exchange for Weapon Attachments, Outfits or Vehicle Paints. This can be done either in the inventory or Customize screen."

- In-Game Description

Vouchers are a gameplay feature in Battlefield Hardline, available in Battlepacks. Once obtained, they allow the player to unlock the specified item for any weapon or vehicle, though this may only be used once per voucher. For instance, the PK-AS voucher would allow the player to unlock the PK-AS holographic sight for one weapon of their choosing for no extra cost. Once used, however, the player may not use it again to unlock another PK-AS for a different weapon.