The ORLIK code is both an invite and bonus code. Tested it, working on EU. It gives out this mission:
Poland Defense Mission
Rewards
12500 XP
10 Bread with Smalec
5 Large Repair Kits
5 Large First Aid Kits
5 Automatic Fire Extinguishers
Objectives
Play 10 battles
Deal damage at least equal to the hit points of your vehicle
Restrictions
Only in Random Battles
Only in Polish Tier IV-X vehicles
Once per account
You must activate the “ORLIK” code
Important: If you are already in the game before activating the code, please make sure to log out after activating the code and then log back in to activate the mission.