Hey @Fregatpro ,
I would reformat the flash drive. To do this, go to Disk Utility, select the drive itself (not the partition, but the drive itself) then press the "Erase" button at the top of the window. In that window, rename the drive to "USB", then select "Mac OS Extended (Journaled)" and "GUID Partition Table".
Create the installer again and let me know what happens.