You cannot place lantern in walls
From the 18w46a article:
The lantern can be placed either hanging under a block or on top of a block
MC-139392Lantren can't be placed on wallsYou cannot place lantern in wallsResolution:UnresolvedStatus:OpenConfirmation Status:UnconfirmedLabels:Affects Versions:18w46a
MC-139392
![[Mod] Asteraoth](../../../data/avatars/users/92886.png){kind=small}
From the 18w46a article: