I have received a vouch copy from this OP.
First of all, It only works on US iTunes accounts. also its only redeemable on mobile devices. (I have Indian itune account, and had to switch to US account to redeem the code)
You will receive the voucher code on email, which you can reedem at App Store from mobile. The seller was quick and no doubt the code works.
its 9.99$ voucher code for in app purchase. You will receive 1200 gems.
BUT, I'm not sure how the codes were obtained. So there might be the possibility that supercell or apple may revoke the gems purchased through these codes. (yes, it happened with many users. but with different carding method)
Screenshot of redemption:
https://imgur.com/uREp4J7Screenshot once you open the COC:
https://imgur.com/UeKD2jZGood luck for your sale OP.