The Missing Dollar Riddle

Three friends check into a hotel room.
It costs $30, so they each pay $10.
Later, the hotel realizes the room should’ve only been $25.
The bellhop returns $5, but can’t split it evenly,
So he gives each friend $1 back and keeps $2.

Now each friend paid $9 (3×9 = 27), plus the $2 the bellhop kept = $29.
Where’s the missing dollar?