pay on怎么解释？???和pay for 的异同？

pay on certain time/date
You need to pay on the 25th of this month.

pay for certain person or certain goods
I'll pay for him for the book he bought.

pay on 在...上付款
Do I pay on the bus?
在车上付款吗？

pay for 为...付款
Let me pay for it.
让我来付费。
意思差不多,但pay for 更常用