I downgraded my O3DS with d0k3's SafeInstaller with no issue (https://github.com/d0k3/SafeA9LHInstaller/releases/tag/v1.5.2mod2). It can launch the Gateway menu without issue.Actually, you can't follow that guide. You need to go back to a clean 9.0-9.2 sysNAND backup, and use the v1 A9LH payload files, with the older SafeA9LHInstaller.
v2 doesn't let you downgrade it.
View attachment 52660
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Got that info from here: https://gbatemp.net/threads/a9lh-choose-bin-file-to-load.430461/#post-6440943
I used of course payload_input and data_input from a previous version of Plailect guide.