Voucher code can be redeemed when you check out your order and the order amount should be over the voucher amount (No maximum usage per time). 

However, there is a Maximum redeemable limit of Coin for a single order is 10% of the order amount. 

Currently you can also withdraw coin to cash.  For how to withdraw, kindly refer to : https://kilimall.freshdesk.com/support/solutions/articles/35000110007-what-is-kilimall-coin-formerly-known-as-cash-rewards-cashrewards-