What did Absalom do when Joab twice refused to come to him?

Answer: Set Joab's barley field on fire

Absalom told his servants, "Joab's field is next to mine, and he has barley there. Go and set it on fire!" Then Joab came to him.

“Then Absalom said to his servants, “Look, Joab’s field is next to mine, and he has barley there. Go and set it on fire!” And Absalom’s servants set the field on fire.”— 2 Samuel 14:30 (BSB)