When I update my iphone X to IOS 14.8,there always remind that "software update failed ,there was an error when download the iOS 14.8

To update all of these requirements must be met:

• You must have sufficient free storage; probably at least 4 GB (5 for iOS 15)
• You must be connected to a Wi-Fi network (and not a personal hotspot) unless it is an iPhone 12 series with an active 5G network connection
• The phone must be charged to at least 50%, and preferably plugged in so it stays above 50% during the update
• The phone must not be in Low Power Mode
• The phone must not be connected through VPN
• The phone cannot be in Airplane mode