At the time of update it paused why

There are many possible reasons an update will pause. Here are the most common:

• You do not have a Wi-Fi connection (you can’t update over mobile data or personal hotspot, only Wi-Fi)*
• Your phone is in low power mode
• Your phone is not charged to above 50% ideally, it should also be plugged in to assure it stays above 50%

There is more troubleshooting information here→Updating iOS: common issues and solutions - Apple Community

*If you have an iPhone 12 series and a 5G network connection you may be able to update using 5G.