Paypal Credit Pay differed?

[ThinkPad560X]

I am just paying off my paypal credit and credit card. These are the only things I have that is debt.
I used the credit card to buy food and such and is at $900 (Was at $1800) The card is closed and just paying on it till paid off.
Paypal credit is at $2999.00. I am getting rid of it once it is done and just going to buy what I need as things get worse. I am done collecting PCs now as it has become a back hobby and only can afford to pay bills and food.

For the question. It says to pay the differed amount to avoid interest, $340 "Random amount" But next month is the last 6 months before $1500 is due. Paypal rounded the purchases up into that one month for that month and it all expires Feb 15. I bought at different times though in the month. From what I been reading online and from what people told me. I want to pay $500 on the $340 but everyone says paypal will put that toward a later purchase and may not go toward the next month $1500. If that is so then should I just wait till the Feb pay the differed payment comes in?
Everything that was bought on PayPal was $100+ to get the 6 months no interest if paid in full. So there is no paypal purchases of $99 or less.