Hi everyone,
I come back with my unsolved problem... (several hours of tests and researches on internet).

I have bought a Darwin BabyApe without receiver.
So i've decided to buy a Radiomaster R81
I have the FrSky Taranis X9 Lite and the external XJT Lite module.

Problem : impossible to bind the Drone with my RC

I've controlled the wires soldering from the R81 to the FC on BabyApe and everythinks is correct !
I've binded the R81 with an old RC (Emax) and the binding was successfull (red light on R81 is blinking)
On betaflight, i've selected "Serial base receiver (SPEAKSAT, SBUS, ...)" and SBUS
On my FrSky Taranis X9 Lite i've selected Internal Module = OFF and External Module = XJT Lite D8

So it seems that the R81 receiver is fonctionnal and the XJT X9 Lite also (i use them with another drone)

Must i set another settings on betaflight
Can anyone help me ?
Regards

Finally, I've decided to buy a FrSky Archer RS and everything work fine !
So... my advice : "Don't buy the Radiomaster R81 !!!"
Regards