1. WELCOMEBACK5 - rewards are 320 Stamina, 5 Ritual Tokens, 50 Power Essences, 50 Bless Stones, and 50 Enchantment Stones.
2. Summer2017 -
These 2 codes are the most well-known. Almost everyone knows about these codes already. But there are more:
1. LuluLOA2 - rewards are 1000 Souls, 500 Stamina, 1k Diamonds, and 1 Primal Crystal.
2. Lato - rewards are 50 Palace Energy, 100 Stamina, 20 Azuruos Shards, 50 Lvl 1 Exp Scrolls, and 5 Pray Tokens.
3. Sommer - rewards are 100 Stamina, 50 Palace Energy, 5 Pray Tokens, 20 Azuruos Shards, and 50 Lvl 1 Exp Scrolls.
Try them and see if they work for you. They worked for me fine, no reason these shouldn't work for you. If you know of any codes not mentioned above, please do share in the comments below. Have fun!!!