I have my samsung galaxy a6+ (2018). I tried to install a GSI to my phone since it has a /vendor partition. First, I did OEM unlock in developer settings. It told me to reset the phone in order to do that. So I did press the reset button. As I was on stock rom, the phone turned off, and showed the blue-background android logo saying "Erasing...".
After its screen turned off again, I pressed the key combo to go to download mode. FRP and OEM UNLOCK was both off. And flashed twrp which I had compiled. The problem appeared then. After flashing, it rebooted, show the samsung logo with "Recovery is not SEANDROID enforcing, Set Warranty Bit: recovery", and screen just turned off.
Even backlight was not on. I tried multiple times to enter download mode, by pressing the key combo, but no luck. It just shows same "Recovery is not SEANDROID enforcing, Set Warranty Bit: recovery" and screen just turns off. But why? Did I do something wrong?