No need to downgrade, I have Nougat 7.1 with FRP lock, upgrade it to Oreo 8.1 then FRP unlock without any problem
This combination and unlock file work with Oreo and Nougat firmware
link removed as I do not have enough post count yet
These two files are around 2GB, work with Nougat or Oreo firmware.
1- Boot to download Mode ( Power + Volume Down + Home )
2- Flash the combination file first with Odin 3.13 in AP slot ( Older version of Odin will fail to flash ). You device will boot to Factory Mode after flashing successfully.
3- Boot to download mode again, then flash the FRP unlock file in AP slot.
After flashing and reboot, your FRP lock will be gone.
If you don't know your firmware version, boot to Recovery Mode ( Power + Volume Up + Home ), the build version will be at the top.
If you do something wrong in Download Mode, don't panic, Power + Volume Down will exit this mode. Many don't know how except pulling out the battery cable.
I started with the Nougat build RF1, upgraded to Oreo RK5 to unlock FRP.
The last 3 characters of the build will tell year and month of release
RF1 ( R=18, F= 6 ) = version 1 released on June 18., Nougat OS
RK5 ( R= 18, K = 11 ) = version 5 released on Nov 18 , Oreo OS
This Oreo build RK5 is US version but the unlock files will work with any region as Samsung tablets sold anywhere , all having the same mainboard, firmware will be customized for certain region.
Update:
I have a tab A with Nougat 7.0 build QL1 , factory reset in Recovery Mode to trigger the FRP lock, then use the combination and FRP unlock, it will unlock FRP and the firmware will be RJ9 of Oreo. The tablet will update to the current RK5 by itself via wifi, around 107MB.
So don't need to upgrade firmware if you are having Nougat with FRP lock.
this worked! thank you
I googled for hours and hours and spend days trying a lot of complicated steps and could not believe how easy it ended up being with above steps
Thanks again Beut