DB9 -> USB issue with spectrum-Amiga not using the same button

[guilders]

Hi All,

I have purchased DB9->USB adapter from this website ([https://www.consolekabels.be/fr_FR/a-52585783/manettes/adaptateur-usb-atari-commodore/](link url)).
It works fine.
Recalbox identifies the joysticks as "hexagons.de Retro-Joystick".

My goal is to use old Suzo The Arcade joysticks to play Spectrum and Amiga games.
As you might know, these joysticks only have one button.
I had to configure it to be button A, so that I can easily navigate in recalbox's menus and select a game. No issue to play Amiga games but it looks for the spectrum though, that it requires button B to be configured instead of A.
As the adapter has to inputs, I tried to configure one joystick with button B and the other with button A, but it looks like it considers both with the same button.

How can I solve this ?
I looked into recalbox.conf, but couldn't find anything to modify. Or maybe in the below figures is it possible to tell if it uses A or B button?
emulationstation.pad0=03000000c0160000dc27000001010000:hexagons.de Retro-Joystick
emulationstation.pad1=03000000c0160000dc27000001010000:hexagons.de Retro-Joystick

Or maybe is it possible to tell the spectrum emulator to use button A instead of B ?

Any help welcome