Hello,
after this want to my customer choose how want to pay, all after press buy or some in 2month later or 3month, with situation that i set in product setting , and for someone want to buy all in cash price be "n" some wnat to pay whole money in 3 payment price set manually "n + 5%permonth or manaually added"
As it's said on that thread :
www.hikashop.com/support/forum/payment-m...ay-later.html#224321
You could create a "collect on delivery" payment method and call it "pay later" so that the customer could choose it during the checkout.
Also, for the payment "plan" you'll probably just have to use characteristics, to dynamically change the value of your product price based on the selected "Payment plan".