Open Settings on your iPhone or iPad
Tap your name at the top
Tap iCloud
Tap iCloud Drive or the app that is paused
Turn Sync this iPhone on if it is off
Check that you are signed in to the correct Apple ID
Connect to Wi-Fi
Plug your device into power
Turn off Low Power Mode
Make sure you have enough iCloud storage
Restart your device
Open the app that is syncing and leave it open for a few minutes
Check for any pending software updates
Sign out of iCloud and sign back in if syncing is still paused