Turn off your Xperia device. Hold the Volume Down button and connect it to your PC via USB. The LED should turn green.

: Download the latest release (v20 or newer) directly from the official developer thread on XDA Developers.

I’ve noticed a lot of people asking for the most reliable way to flash stock firmware on older Sony Xperia devices. After testing various versions, remains the "best" and most stable release for devices still using the S1 protocol (Xperia XZ, X Performance, XA2, and older).