Been getting strange messages while trying to unlock bootloader

I've been following the official Sony method to unlock the bootloader, you can see that procedure here. I have downloaded and installed the SDK Manager, then replaced the fastboot driver for Sony phones like they say, then I can also successfully put my phone into fastboot and my computer also recognizes it as "S1Boot Fastboot" but when I try to update the driver to point it to use the driver supplied to the SDK, I get this message when trying to install it (in the driver error.png). I'm not sure if it's trying to say that it won't work or something. So I proceeded to the command prompt stage (that's in cmd1.png) and entered fastboot. That worked. Then I entered fastboot devices and get a new empty line, whereas I'm supposed to get some text returned (see cmd2.png). Trying to enter the command to unlock bootloader after that doesn't seem to be doing anything (see cmd3.png).

So, anybody have any suggestions?

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