Hello, Alain!
My French is too poor to answer your question. So I try to do it in English.
There should be no real problem. I have done it several times without any hassle.
Switch on your COCKPIT SX TX and open the buddy menue (icon right hand button corner) and activate "teacher" (tick the box left hand top corner), then tick the box for "seaching pupil/student". Now switch on your SMART SX in binding mode (press black button and then switch on the TX) - the corona should blink fast. Position the front of both TXs head to head at a distance of about 20 cm. The link is estalished when the SMART stops blinking fast.
It might be that the binding process needs some time. I have tried it today and the first attempt took about 2 minutes. Further attempts needed only a few seconds. Only hell knows why there can be such time differences. You possibly need some patience!
Good luck!
profimc