I recently had some issues adding an admin user to a Facebook page I created. A quick Google search told me I wasn’t the only one. It took me some time, but I finally figured it out.
I had the other person “like” the page. On the “likes” list, you see a little button to Make Admin next to each user. Clicking it did nothing. Going to manage admins and adding the person by name did nothing. Frustrated, I went over to Google and found no answers, just more people as perplexed as me.
Not being one to give up, I kept at it all day and finally figured it out. If you are not “friends” with the person you are trying to assign admin rights to, then you must use the Manage Admins page and put in their email address, not their name. It doesn’t matter if they have liked the page or not. If you don’t have a connection to them, you need the email address they used for facebook. Simple as that.