Microbit Driver Expansion Board & Stepper Motor

Hello everybody. 

I come here because I have trouble to make Stepper motors turn with my Micro:bit and its driver expansion board. 

To make it simple, I need to use stepper motor to craft a 3D scanner. 

However, when I wire the motor to the board as shown on the photo in the zip, and when I put the code given on the wiki for the board (https://github.com/DFRobot/pxt-motor) in my microbit, the stepper motor does not turn.  I hear it functionning inside, but it does not turn. 

I use a 28BYJ-48 Step motor.

I hope you can help because I really don't understand where I've failed

Thanks !!