Thanks for your answers. I did not understand that it was already included. I thought I needed to add something to get the “LEGACY” mode working.
As mentioned by heavy-matill, I did set the variables, I used a 6 number PIN and it did not work on my iPhone 7. I did not try a computer nor the 000000 PIN (I now realize I should have). Anyway, I always got a timeout error on my iPhone. (edit: BTW, the Bluetooth pairing worked great without the LEGACY + PIN variables… I just wanted an extra layer of security because my use-case is similar to Snellie’s)
After reading the documentation, I now understand it is not supported by iOS.
From the attached document (thanks @heavy-matill), it seems that out-of-band pairing method are still permitted. I understand it is probably not implemented, but that would work for me.
@robertgzr : I did install the latest version I could on my raspberry pi 3. I also tried both 32 and 64 bits version.
Anyway, thanks for your answer, I now have a better understanding why the bluetooth was not working and how the system works.