WoW accounts must be in the same game region in order to be connected. For example, if you have a European WoW account but received an invitation from a friend in the Americas & Oceania game region, you will not be able to connect those WoW accounts; you would first need to create a WoW account for the Americas & Oceania region.
Once you accept the invitation, the player who recruited you will be able to see your BattleTag, your online status as it appears in Battle.net, and your WoW subscription status.
You must have a new WoW account, a WoW account created in the past seven days, or a WoW account with no paid game time within the past two years to be eligible.
Additional restrictions may apply. For details, please visit this Article