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A list of hardware interfaces will appear. Select or Sony Fastboot Interface .
Installing the is the "gatekeeper" step for Sony device customization. While Windows' security features make it slightly more complex than it used to be, disabling signature enforcement and manually pointing to the driver files will solve the issue 99% of the time. Once the blue LED stays lit and your PC recognizes the S1 interface, you are ready to flash kernels, recoveries, and ROMs to your heart's content.
This usually points to a hardware compatibility issue, frequently caused by USB 3.0/3.1 ports or faulty cables.