Hi Jossa,

The manual is poorly written and doesn't specify the voltage levels. It looks like there are opto couplers on that board (small 4 pin chips). So probably an output sinking to GND will turn on the 5V Opto LED. KFLOP can sink a +5V signal to GND fine, but when it goes high it may only be ~3V which will still apply ~2V to the opto and it may not turn off. So as stated earlier by others I suspect you may need a level shifter to higher levels closer to +5V. Something like this might work:

JY MCU 5V 3V IIC UART SPI Level 4 Way Converter Module Adapter | eBay

You would need to buffer the PWM as well. You will also need a GND connection. A PWM signal is a pulse that is a fixed frequency (like 1KHz) but is high some percentage of the time. The higher the percentage the higher the speed should be.

There is an example called PWM1KHz.c that will output a 50% duty cycle at 1KHz on IO26. You might switch your wiring to connect the PWM signal to IO26 to make things simpler.

If you get that to work and run at 50% speed then we can give further instructions on how to vary the speed programmatically and such.

I doubt if you can set what speed a 10% duty cycle will give you. It will probably be 10% of the full motor speed.

HTH
Regards