I'm pretty sure you missed the first step. Press and Hold L then enter the cavern in the underground, every time you exit the cavern you need to repeat again.
IMPORTANT! For those facing "Failed....device_key_4x" just edit the device_key_4x to device_key in your prod.keys. Wasted 3 hours trying to figure this out.
Not yet but theoretically if they implement support for gen 3 then you are able to do that but certain data will not be accurate compared to actual pal park since it will be something like this -> delete/copy pkmn from gen 3 -> duplicate/paste into chest.
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Awesome! Hopefully you can implement for 3rd Gen too as gbarunner2 (@Gericom ) is doing great since gba .sav located in sd card and pkmn-chest able to search for .sav file in the sd card.