Why downloading paused

Check out the help in this Apple support article > If you can’t download or update apps on your iPhone or iPad - Apple Support

Also,

If you are updating your iOS and it pauses during the process,

Make sure you:

• Are using a WiFi connection (not a hotspot).

• Have your battery charged at least 50%.

• Are not using a VPN connection.

• Do not have power save mode turned on.