There are eight possible causes for a Facebook friend request being declined.

Facebook is now among the most popular social media sites, and it has the largest user base. The ability to add followers who can see your updates and have theirs seen by your friends is a major selling point. So, you might have run into a scenario where you went to add someone, but the option to do so suddenly vanished.  

You shouldn't assume that just because you can't add someone on Facebook that they have blocked you. Here's a list of some of the other possibilities that might be at play in your situation.  

First, the Security Options They've Chosen

The Facebook privacy settings of the person you're trying to add are usually the culprit. While adding someone on Facebook, there are a few privacy settings that could prevent that from happening. You probably won't be able to send this person a friend request if they have their Friend Request privacy set to "Friends of Friends" and you don't share any mutual friends with them.  

In any case, you can always message them and politely request that they send you a request if you're set on doing so. However, you should know that since you aren't friends, your message will be delivered to the recipient's Message Requests inbox. As a result, they may not see your message for some time.  

The Account Is Now Inactive

Also, if the person you're trying to add has deactivated their account, you might not be able to add them. Unless the account holder completely deletes it, it will likely persist in some form after this action. However, as long as their account remains inactive, nobody will be able to send them friend requests.  

Even after a user has deactivated their account, it will still be visible upon subsequent login. Even after deactivating their account, they can still access Messenger, so you can still send them messages.  

There is a block on your access.

A Facebook user can prevent another user from seeing their profile or contacting them by blocking their access. You won't be able to see their profile, posts, photos, or comments, and you won't be able to message them, either. Inquiring about a potential message recipient's response time will reveal whether or not they have blocked you. No communication means you've been blocked.  

#4 You Blocked Them

If you're trying to add someone but are unable to do so, it's possible that you've accidentally blocked them. You may have forgotten if it has been a while since you last did this.  

Facebook maintains a block list so you can see who you have blocked. Settings & Privacy > Settings > Blocking is where you'll find this. You can see if the person you're trying to add is already on your blocked list by visiting this page. Choose the Unblock link that appears next to their name to remove the block.  

Fifth, They Can't Acquire Any More Friends

As it turns out, Facebook limits the number of friends each user can have. You will no longer be able to add someone as a friend if they have more than 5,000 on their list. A Facebook alerting system should inform you when a user reaches 5000 friends.  

You still won't be able to add someone who has already reached their friend limit if they send you a friend request. The request will not be processed if accepted, and neither of you will be added to the other's friends list. Nonetheless, you can still contact anyone with 5,000 or more friends.  

6) You have already asked for something

Since sending a request to someone disables the "add" button until they accept it, you may want to see if you've already contacted them before sending a request. It is easy to forget about a friend request if it has been a while since you sent it and they still haven't added you.  

Even after sending a request, you should be able to send a message to the recipient to remind them or request that they add you. It's possible that the person has forgotten about the request or that it was buried under a mountain of other friend requests.  

Seven. You Were Refused What You Asked For

A second possibility is that the person has already turned down your request. If you've already sent a friend request but still see the Add Friend button, it's probably because they rejected your request. If the Add Friend option is still available, you can try sending another request.  

To add insult to injury, if they have certain privacy settings, you may not be able to add them even if they sent you a friend request and you denied it but now want to add them. If they want to be your friend, they'll have to send you a request again.  

Their Facebook access was limited for some reason.

If a user is reported to Facebook multiple times or is found to be in violation of the Facebook guidelines, the user's account may be temporarily disabled. Some examples of possible durations are several hours to several weeks. In this period, the individual is prohibited from engaging in certain actions.  

You might not be able to add a new member because of this. A possible solution is to wait a little while and then try again to see if it works. It's possible that you won't be able to reach the person via Facebook Messenger if Facebook has disabled that feature for them.  

Completing a Facebook Friend Request

Frustration is understandable when adding friends or interacting with others on Facebook doesn't go as planned. If you find that this is happening with every friend request you make, or if you keep getting adding friends errors and can't figure out why, you can always try contacting Facebook support to see if there's something else wrong.  

If you have any questions about Facebook, Twitter, Instagram, or any other social media site, hopefully you can find the answer here.