If your carrier refuses (e.g., you bought a locked phone second-hand), legitimate services provide a for $10–$30. These are not software downloads; they send a code to your email.
Stay safe, and enjoy your unlocked Sony Xperia the right way.
Unlocking a Sony device involves different "tools" depending on whether you want to unlock the bootloader (to install custom ROMs) or a network-locked 1. Official Sony Bootloader Unlock (Developer Tool)
For newer Sony devices (Xperia 1 II, Xperia 5 II, and later), the older Flashtool sometimes struggles with driver compatibility. New Flasher is a command-line tool that handles the flashing of the newer partitions (like super and odm ) found in modern Android versions.
Open a command prompt / terminal inside that folder.