What did the nearer kinsman remove to confirm he was giving up his right to redeem?

Answer: His sandal

In former times a man would remove his sandal (KJV: shoe) and give it to the other party to make a transaction binding.

“Now in former times in Israel, concerning the redemption or exchange of property, to make any matter legally binding a man would remove his sandal and give it to the other party, and this was a confirmation in Israel. So the kinsman-redeemer removed his sandal and said to Boaz, “Buy it for yourself.””— Ruth 4:7-8 (BSB)