The conditions for when wall of fire deals damage, after the initial casting, are as follows (emphasis mine):
One side of the wall, selected by you when you cast this spell, deals 5d8 fire damage to each creature that ends its turn within 10 feet of that side or inside the wall. A creature takes the same damage when it enters the wall for the first time on a turn or ends its turn there. The other side of the wall deals no damage.
This is a bit confusing, because it seems like there might be two separate effects that can each deal damage to a creature that ends its turn inside the wall itself. Specifically, if the creature starts its turn inside the wall and remains in the wall for its entire turn, it looks like both effects would trigger at the end of its turn, dealing a total of 10d8 fire damage. (It also looks like a creature that enters the wall on its turn and remains there might take 10d8 total, but not all at the same time.)
Is this intended to deal double damage to a creature that spends its entire turn in the wall, or is the wording simply a bit redundant? How much damage does a creature take if it spends its entire turn inside the wall of fire?