The following error message appears while backing up your device, even though finder says there is enough disk space:
"There is not enough free space on [disk name] to backup [device name].
Required: xx.xx GB
Available: xx.xx GB"
iMazing does not calculate purgeable space as available space. The reported available space is the Available space - Purgeable space.
E.g.: 47.53 GB available - 21.63 GB purgeable = 25.88 GB reported
Free up storage space on your Mac, by clearing your disk's purgeable space:
Apple menu () > About This Mac > Storage > Manage > Optimize Storage
For more information, see Apple's article on how to free up storage space on your Mac.