It asks you to confirm the unblock. Do it by clicking the Confirm button on the popup window. When you unblock someone on Facebook, he/she will start seeing your posts on the timeline. In this ...

When you block someone, the first thing that Facebook does is restrict the blocked user's access to your profile. The user ...

If you change your mind and want to block them again, you'd have to wait 48 hours before you can do so. How To Unblock Someone On Facebook Messenger Follow these steps to unblock someone on ...