You will receive 200 in-game Tebex Coins + a bonus 50 Tebex Coins which can be used to purchase various in-game items/vehicles at the in-game Tebex Shop.
After you have purchased, wait 2-10 minutes and then use this command in-game to redeem your Tebex Coins -
/redeem (tebex transaction id)
EXAMPLE: /redeem tbx-632425bf1231-etc123