I fixed that with "fastboot flashing unlock"thx for the reply ! , i did what u told me to do but i have the following message :
Setting current slot to "a"
FAILED ( remote: Slot change is not allowed in lock state
)
finished total time : 0.002s
And my phone is the same as before ... Why ?
And then "fastboot flashing unlock_critical"
I'm not 100% sure that's how you write the commands, but after I did that, I was able to set active slot to "a".