Maybe the issue with the keyboard typing numbers instead of letters can be easily solved by restarting your device. Unplug it from the power cord and plug it in after a couple of minutes.
If this error appears again, then feel free to check out the other solutions.
It is possible that the USB port in which the keyboard's USB cable is plugged in doesn't work properly. Unplug the keyboard from the current USB port and plug it into another one.
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