Making Extra Payments on AppleCard

Just made a monthly installment due May 30. Now on June 2 I would like to make an extra payment; however the wallet will not allow a $500 extra payment unless I make another installment payment. Next Installment payment is due on the June 30. Why are we being held hostage by GoldmanSachs on making additional payments when we want and how much we want? My first time using this AppleCard for purchasing Apple products interest free. I will not be using AppleCard for future Apple purchases and will NOT recommend AppleCard to my friends.