Which phrase means "given away for free"? drop the ball get cold feet in the same boat on the house

"on the house" = "given away for free."

"Here," said the waiter when he put the appetizer on the table. "It's on the house."

Explanation:

drop the ball = made a mistake (you let someone down)

cold feet = scared/afraid

in the same boat = in a similar situation as someone else