What did Nahash the Ammonite demand as the price of a treaty with Jabesh-gilead?

Answer: To gouge out their right eyes

Nahash wanted to put out every man's right eye to disgrace all Israel. Saul rallied the tribes and rescued the city.

“Then Nahash the Ammonite came up and laid siege to Jabesh-gilead. All the men of Jabesh said to him, “Make a treaty with us, and we will serve you.” But Nahash the Ammonite replied, “I will make a treaty with you on one condition, that I may put out everyone’s right eye and bring reproach upon all Israel.””— 1 Samuel 11:1-2 (BSB)