"Why not let your allies manage your defense? Invite them to send you some defensive Mercs!"
The Friend Watch Post works exactly the same as the Watch Post the only difference is that you can't fill it up yourself. Only your friends can send you troops to fill this Friend Watch Post. Just like the Watch Post you can't send Gentle Healer and Hezarfen to the Friend Watch Post.
Req. CC Lvl
How to send mercenaries to your friends
When you are going to visit your friends to help them or to simply collect Recon Points, or you want to send your friend a gift, you can also "Support" your friends. When you click on support you will be able to send mercenaries to your friend's Friend Watch Post.