Sony Xperia XZ1 (sony-poplar)

How to enter flash mode
Enter Developer options on Android and enable OEM Unlock

Unlock your bootloader by following instructions here: https://developer.sony.com/develop/open-devices/get-started/unlock-bootloader/

Hold PWR and Vol+ until the LED becomes blue. Congratulations, you've entered fastboot.

Installation
Just your standard "pmbootstrap flasher" procedure