Here is the binding procedure for external Futaba receiver:

Note:  Please make sure the setting in Betaflight is correct. If there is confusion about setting, we suggest you flash the Cli that we shared in our website. 

How To Bind:

1) Press and hold the bind button on receiver and connect the drone with battery. Green LED with fast flicker means entering the binding mode. 

2) Choose "BIND" in the transmitter.

3) Binding is successful when green LED is on.

4) Power on again, green LED is on, which means the quad is functional.