Paypal Credit Payment

Description

I tried contact with support but they cant answer me, so let’s see if you can help me
I already had a paypal credit buying of xxx pounds, that I am paying monthly, by direct debit, every month I pay « 1 of 12, 2 of 12, 3 of 12, etc… »
Now I bought on paypal credit a buying of yyy, that I have to pay in 3 months or I’ll need to pay interest, so, here is my doubt:
I want to make a payment of yyy, to pay the whole value of this buying, but once I have to paypal credits running, I am afraid of pay yyy (I can’t choose which paypal credit I am paying, I can just choose the whole value xxx+yyy or pay a value I want to pay), but as was saying, I am afraid of pay yyy and it understand that it is from the whoe value (xxx+yyy) and then it starts to charge interest from the second shopping, so, what I want, pay the shopping of yyy only, and let the other one running as it is