If you had this message only once, consider, did you remove your Google A/C, locks, passwords and all then factory reset already?
If you are seeing for a second time it is telling you to do all that!
If you did all that it is a red herring and you take your lead from Odin.
Only once. After some reboots, Samsung Anroid starts again.
Had a good friend over today who had done this many times before. We were even able to organize a pit file. We worked a lot of hours the whole day, but no success. Sadly.
Conclusion: It does not work. We have tried everything that was known to us and possible. You can not install a customrom. I think I will have to give up a tablet with a heavy heart.
For last chance, test the link from upper post: https://forum.xda-developers.com/t/guide-17-06-2019-rmm-kg-bypass-root-install-twrp-on-exynos-samsung-after-2018.3747535/
It is known that you must lift the lock āPrenormalā before you can flash the phone. (Official binaries excepted.)
Please read the whole post and updates by @corsicanu. He only tells us it is good for pie! Extract and open the .zip and read all the contents, and check that they will overwrite some lock that you can see is applied, Edit, better idea.
Here are 2 lines from the patch, much of the rest of the patch will try to harmonise /system and /system/vendor following that intrusion.
rm -rf /system/priv-app/Rlc 2>/dev/null
rm -rf /system/priv-app/KnoxGuard 2>/dev/null
I cannot tell you that Warranty void = 0 would survive that!
I say, better to ask Samsung first - they will know - then to look for the lock before such an intervention. At a minimum I would describe your situation and ask on the xda thread.
Please check again, but with Warranty Void = 0 the phone is still potentially returnable!
Later, also before an intervention that is not definitely specified for your device:
adb shell getprop
I suggest you search that command and tell me how far you can get on your own looking for locks.
to give up a tablet with a heavy heart.
If that includes a return you must not change Warranty Void = 0!
Edit - just one more thing is bugging me!
Apparently, the device was originally intended for France.
Please can you tell me how you deduced this? From Samsungās point of view, in that case, the intended market would surely have been EU? (Xiaomi require their devices on line for periods of 7, 14 days, or more. New generations of Samsung may be moving in that direction.)
Iām sorry to say I think you guys are right, itās not possible or certainly damn difficult to get TWRP onto the Samsung Galaxy Tab S5e SM-T720
Getting /e/ or Lineageos as a further step would be easy but this seems to fail in so many ways just to get TWRP onto it.
I have been trying to do this from Linux terminal with heimdall. First was getting
ERROR: libusb error -7 whilst sending bulk transfer. Retrying...
I managed to cure that with the following unmerged pull request for heimdall :
ā¦but then when I went to flash TWRP to recovery from download mode like this :
sudo ./Heimdall/build/bin/heimdall flash --RECOVERY twrp-3.5.2_9-0-gts4lvwifi.img --no-reboot
ā¦it was complaining about OEM lock.
So I realised I had not unlocked the two things which need unlocking as someone else wrote and followed that initial step.
Then I realised Iād skipped vbmeta.tar so downloaded it, unpacked it and ran :
sudo ./Heimdall/build/bin/heimdall flash --VBMETA vbmeta.img
It wasnāt happy :
Downloading device's PIT file...
PIT file download successful.
Uploading VBMETA
100%
ERROR: Failed to confirm end of file transfer sequence!
ERROR: VBMETA upload failed!
Ending session...
Rebooting device...
Releasing device interface...
So I think this thing is in the too hard basket, at least to do from Linux. I donāt really have Windows sitting around except in a Virtualbox and that somehow sounds even less robust. Anyway, will watch this thread and see if anyone works it out and try to put that thing back in the draw and not take it out again, have lost hoursā¦
I read somewhere, someone made a comment to choose brand other than Samsung if you are trying to install ROMs (from Linux). This is the second time I have had misery with Samsung and Linux, but have had other devices where getting to the TWRP stage is so easyā¦
Hi @bear sorry to hear your story! So you have managed to get past the error 7 problem (?).You probably read elsewhere here that error 7 frequently occurs when a change of Android version is attempted in the flash. As a rule of thumb /e/ should be installed only on a Samsung most updated ROM. (Having the factory reset just before one starts work is always a good precaution!)
Please can you tell us the Android versions you are starting with and aiming for?
Did you study the Odin screen for clues? Would you like to share a picture here?
@aibd yes by using that unmerged fork of the heimdall terminal program, I got past the error 7 problem. Then the bright blue download screen responded as if it had allowed something to be flashed with a progress bar, but it moaned in bright red letters about OEM lock and later about something else when I tried to flash vbmeta.img (unpacked from vbmeta.tar)
Does that even matter yet? Itās still in the TWRP stage. I stopped trying to use Odin a while ago and stuck with that terminal heimdall program. Also deleted that Odin program, but if someone really thinks that is the key, can they post a link from which Odin for linux can be downloaded?
You have a āmore modernā phone. You do not want to hear about fixes that would work on a similar device 2 years ago!
You could always read up about Android verified boot yourself to help understand the increased strength of these barriers in Oreo/pie/10/11. Disturbing recovery is just as significant to verified boot as system!
I do not think Linux, Odin is a thing. I have faith in Heimdall.
Available in current Debian: heimdall-flash-frontend. Gui also available https://glassechidna.com.au/heimdall/ (I didnāt test.)
tablet (267.2mm or 10.5") S5e SM-T720
From the specs online Iām seeing āAndroid 9.0 Pieā but canāt bear to switch it on right now to confirm that.
Ok good, so someone else also thinks heimdall should be good enough. I cloned the repo, retrieved and checked out the unmerged branch, then did the things they said to create a heimdall command:
mkdir build
cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make
Although Iām running Debian, donāt think that that thing from the Debian ppa will do this without those errors with the ā-7ā
If TWRP would flash, the rest would be easy, Iām sure. I believe that you need to get that vbmeta.img or vbmeta.tar onto it somehow to make that OEM lock error go away so someone please say if they get passed that step.
Thanks for confirmation, SM-T720. Agreed, I see the device delivered as Pie/10.
Sammobile lists Android 10 as the latest firmware for this device. It is probably required that the device is fully updated before start in order to receive /e/ R. (This can be a cause of Error 7.)
I agree on sequence, but you can double check, the order of play is expected to be as our instructions (in OP).
The thing I had been specifically addressing in this thread so far is KG Prenormal.
KG Prenormal would always explain multiple fails. Prerequisite to fix.
Can you tell if it is an issue for you? (Can be read from "Download mode screen).
Edit, re Heimadll frontend, a self-biuld is ideal to be up to date for doing R, great. 
. Seeing your
sudo ./Heimdall/build/bin/heimdall flash
I would be interested to know if you find in Heimdall/build/bin the command heimdall-flash-frontend, it seems to show in his repo. The possible advantage is that the GUI might reveal blockers that would only show with obscure command line options, possibly!
Further Edit, thanks to Installation /e/ sur Galaxy Tab S5e - #38 by piero in this xda thread https://forum.xda-developers.com/t/rom-official-gts4lvwifi-11-lineageos-18-1.4169395/#post-83600521 @LuK1337 provides ā bit more friendly stock ā lineage instructions ā which includes a couple of wise steps, (only after KG Prenormal is lifted.)
I see I accidentally introduced a misspresentation about libusb errors in Heimdall and Error 7 on the device.
In any case of repeated Samsung fails, it is always worth trying another cable!
TWRP is running now fine. The problem was, that if you start the tablet with the power button only the system will be overwriten automaticly. Only if you start with āvolume up + powerā the it is booting to the new installed TWRP.
After that i installed the e/OS package successfully. But the system is booting only in TWRP. i open for this a new thread. 
And finaly e/OS works also on the device very fine. Apparently there was a problem with the system partition. After another wipe it now works. FINALLY