Unlike Google Pixel, OnePlus, or Xiaomi devices, (any model: A7 2016, A7 2017, A7 2018) does not support the standard fastboot protocol. Instead, Samsung uses Download Mode (Odin mode) for low-level firmware operations.
If your firmware is based on GSI (Project Treble) or a pure AOSP build, the developer may have removed Samsung’s bootloader handshake and enabled Fastboot over USB . This is uncommon but possible on unlocked bootloader devices. how to open fastboot mode on samsung galaxy a7 repack