Testing Samsung A3 (2016) a3xelte January 2021 Oreo "dev" build

[aibd]

Here from a Samsung guide,

@aibd

The instruction set to make your first boot into TWRP is often abbreviated for experienced users, but for a first timer would read:

• Please now Force stop the phone – from the current “Download mode”
  • Disregard the (unhelpful) screen message “Downloading … Do not turn off target”
• Use Volume down + Home/Bixby + Power to Force stop.
• Attend carefully, keep holding the buttons - it may take about 7 seconds,
• the instant the screen goes black (black as in off) and before the device starts to restart
• instantly change the finger press to Volume up + Bixby/Home + Power,
• Be prepared for another 7 second hold without relaxing, until Teamwin is seen.

If however the problem is flashing TWRP, you don’t say if you are using Windows or Linux. In Linux (depends on distro) Heimdall probably needs android-udev-rules

https://doc.e.foundation/pages/insufficient-permissions,
https://developer.android.com/studio/run/device.html
https://github.com/M0Rf30/android-udev-rules