Why can't my Friend add Mercenaries to my Army?:SI
In addition to the 3 Mercenaries you can hire daily, your Friends can add to your Army by visiting your Base and clicking above your Mercenary Bar.
You and your Friends can command up to 50 Mercenaries at a time. If your Friend can't recruit a Mercenary in your Army, it means that they have already recruited one.
They can hire you a new one when the previous Mercenary has been defeated in combat.