Backup for iPhone 7 not working

How to back up with iCloud

1. Connect your device to a Wi-Fi network.
2. Go to Settings > [your name], and tap iCloud.
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5. Tap iCloud Backup.
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8. Tap Back Up Now. Stay connected to your Wi-Fi network until the process completes.

You can check the progress and confirm the backup completed. Go to Settings > [your name] > iCloud > iCloud Backup. Under Back Up Now, you'll see the date and time of your last backup.

Get help making a backup or manage your available space in iCloud.

Automatically back up with iCloud Backup

To let iCloud automatically back up your device each day, here's what you need to do:

• Make sure that iCloud Backup is turned on in Settings > [your name] > iCloud > iCloud Backup.
• Connect your device to a power source.
• Connect your device to a Wi-Fi network.
• Make sure that your device's screen is locked.
• Check that you have enough available space in iCloud for the backup. When you sign in to iCloud, you get 5GB of iCloud storage for free. If you need more iCloud storage, you can buy more from your iPhone, iPad, iPod touch, or Mac. Plans start at 50GB for $0.99 (USD) a month. Learn more about prices in your region.

How to back up your iPhone, iPad, and iPod touch - Apple Support

https://support.apple.com/en-us/HT203977

You may also wish to take a look at this support document for troubles with an iCloud backup. If you can't back up to iCloud or restore from iCloud backup failed - Apple Support