You can get the brave dungeon gift code on the unlock.game site. follow the following guide.
1.visit official unlock game website.press login button in top right
2. Login your UnlockGame account or you can register to create new account.
3..Click brave dungeon and confirm the gift code. If you can’t find a brave dungeon, click welfare icon.(The location is at the top of the screen)
4.After you press a claim, you will get a brave dungeon gift code. A pop up will appear on the screen. Use the code in the pop up.