How to unlock bootloader on Samsung Galaxy S6 Lite?

Question

I have a new SM-P610 device that I want to install Lineageos on. I am following the instructions at https://wiki.lineageos.org/devices/gta4xlwifi/install but I am unable to unlock the boot loader.

Under "developer options" on the phone I can toggle "OEM unlocking" and changing this is reflected on the download mode screen which shows either "OEM LOCK: ON(L)" or "OEM LOCK: ON(U)", so obviously Locked or Unlocked, however ON in both cases.

If I try to run the heimdall command to flash the recovery image it prints "ERROR: Failed to receive session end confirmation!" and on the screen "Custom Binary(RECOVERY) Blocked By OEM Lock" is displayed in red.

So how do I actually unlock the boot loader?

Answer 1

I eventually figured it out. The guide says

With the device powered off, hold Volume Down + Volume Up and connect USB cable to PC. Now, click the button that the onscren instructions coorelate to “Continue” and/or “Unlock Bootloader”.

and on the screen the tablet displays

Volume up: Continue

This I assumed was a perfect implementation match for the generic “Continue” and/or “Unlock Bootloader“ description, but clicking volume up will just end up in the situation I described in the question.

However on the next line (which I did not read since I had already found a perfect match...) it says

Volume up long press: Device unlock mode

So the device requires a long press to actually unlock the boot loader (which is not described in the install instructions). I did not notice this line until now when writing the answer, I found the long click information in this xda forum post.

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After the successful unlock procedure the tablet behaved as expected (all apps/settings reset/deleted, it now nags about the boot loader being not being verifiable upon every boot, and the OEM unlocking option in developer options is greyed out with status "Bootloader already unlocked".)