About Charging ZP!

Hey there, i just want to know something very important about Charging ZP from "rixty" with a code of 25$, i see that there is no such a way on the payment method with that 25$ value, there is only this values on the payment method:-

1- 10,000 ZP | US $8.99

2- 20,000 ZP | US $17.49

3- 50,000 ZP | US $42.99

4- 100,000 ZP | US $79.99

and there is no "25$" on them, so i need to know that if i chose the " 20,000 ZP | US $17.49 " what will happen to the rest of the dollars on the code i used?!

i'm sorry but i don't know how can i exactly explain this but, i need to know what will happen to the rest of dollars Lol :D

P.S: it's my first time charging ZP so, help me and i promise it will not be the last time to charge if i got a postieve respond from any GM or MOD or even a helpful community member

Regards.