Introduction
If enabled, Speeder's kernel input allows your mouse and keyboard input to come from a legitimate mouse and keyboard installed on your computer. This is relatively significant because there will be no difference between a key you physically press and a key simulated by Speeder, preventing the anticheat from seeing the input as simulated. In the vast majority of cases, it will just work, and you don't have to do anything. However, if you experience the "failed to initialize" message when starting Speeder, you may have to do some additional work.
What Do I Do if It Isn't Working?
Speeder relies on HID devices to send mouse and keyboard input. If you do not have an HID device installed for either your mouse or keyboard, the initialization will fail, and you will not be able to use kernel input. Fortunately, HID devices are extremely common. Most USB mice and keyboards are HID devices and will work fine with Speeder.
To see the HID devices you have installed on your computer, go to Device Manager and look under "Keyboards" and "Mice and other pointing devices." If you see "HID Keyboard Device" and "HID-compliant mouse," you should be all set.
If you do not have an HID device for either your keyboard or mouse, try to find a USB keyboard or mouse lying around (depending on which you are missing) and plug it in. Chances are it is an HID device and will work fine. Really cheap USB mice and keyboards are almost always HID devices, so, worst case, if you don't have one, you can spend $5 to get one.
If you are unable to use an HID device for some reason, you can set the kernel input line in config.txt to 0, and Speeder will use the Windows API to send input. For some games, this is fine and won't raise any red flags, but for others, it can be dangerous. Always check the [Safety] section for each game.
Other Problems
I've been informed that having Interception installed will cause kernel input to fail. Either uninstall it or set the kernel input line in config.txt to 0.
I've also been informed that Avast antivirus (and maybe others?) can cause kernel input to fail. If you are having issues, I recommend temporarily disabling your antivirus so you can narrow down the problem. Window Defender seems to work fine.