More times than not, what's happening is that you do not have enough storage space left on iCloud. You do have a limited amount of space unless you're paying for unlimited storage through iCloud as part of your monthly phone bill.
Backups may fail due to missing or damaged tapes or backup disk failures. The programs that run the backups are not fool-proof and disk usage may grow beyond the capacity of the backup media. To ensure restores, it is critical to monitor backups daily, have an off-site backup and test recovering data.
Media failure, human error and hardware failure are among the most common reasons backups fail. Learn what you can do to prevent these issues and others to perform legitimate, usable backups. Backup troubleshooting tip: Media failure, human error and hardware failure are among the most common reasons backups fail.
If what's happening isn't because of a lack of space, then the most likely scenario is that your tablet or phone is not connected to Wi-Fi. Backing up your Apple device to iCloud is something that's always going to require a steady connection.
There are only a handful of reasons that an iCloud backup can fail. Typically, it's because the Apple ID associated with the iPhone doesn't have enough free iCloud storage space. By default, each user gets 5GB. The easiest solution comes with a small monthly fee to Apple: buying more iCloud storage.
Applications that do not work well with the backup software. Improperly stored backup media, causing physical damage to the backups. Overly complex backup applications with settings that don't work as anticipated. Hardware issues – all devices fail eventually, including backup devices.
The first thing to do when you see this notification is to try and back it up to iCloud manually. Open Settings and tap on your name at the top of the screen. Then, tap iCloud -> iCloud Backup. Make sure the switch next to iCloud Backup is on.
If restore from iCloud backup failed
Your iPhone backups may fail in iTunes for several reasons: Your copy of iTunes may have been corrupted; you may not have enough space on your computer's hard drive or on the device to create the backup; the Lockdown folder may have been damaged, or permissions reset.
Quick Ways to Fix Time Machine Backup Failed Mac software should be updated. Whenever you face Time Machine restore or backup failed error try restarting Mac. If you use Airport Time Capsule update firmware. Mac should be connected to the same network as the backup drive.
Most people will hit their device storage limit due to iCloud Photo Library automatically backing up photos, while backups from old iPhones and iPads can also consume a large amount of storage space if you never delete them.
Usually, it means that your device is not allowing you to connect to Apple's iCloud verification servers. Most of the time, this problem occurs because of issues that are not related to your Apple ID.