Serial communication working but no motor movement

[A1waysY]

I bought " Stepper Motor Nema 17 Bipolar 40mm 64oz.in(45Ncm) 2A 4 Lead 3D Printer Hobby CNC" and the "Makerbase MKS SERVO42A NEMA17 Closed Loop Stepper Motor Driver" (MKS Servo42A v1.1) on Amazon, assembled it according to the youtube manual on github and connected it via USB to a PC as shown attached. Upon plugging in, the red diode turns on for a couple of seconds, and then turns off. I use RealTerm Serial communication 2.0.0.70 to talk to the driver. Calibration commands, dirpin, maxcurrent, velocity etc. seem to work and yield possibly reasonable values. However, none of the move commands (e.g. "step 1", nor "step 1 16" or "move 300") work, the motor does not move at all, but the commands are accepted as valid. Can anyone suggest a solution?

Help is much appreciated, thanks!
A1waysY