Okay back in December I used Paypal credit to buy my Evga 2080 Super from newegg.   It's a promotional purchase that you don't pay interest on if you pay it off in six months.
 
Since AFTER that purchase I've been adding a heap of other things onto my Paypal credit.  Fans, AIO, parts, Steam game purchases, miscellaneous etc.     So since December I've made about 500 dollars in payments to my Paypal credit.  Now I paid around 700 for the card, and as it's the oldest purchase I expected it to be around 200 left.  700 minus 500 should be 200 remaining right??
 
But I check today after my last 100 buck payment and see there is 500 dollars left on it? What!?  What is going on?  Are they deliberately putting my payments onto the non promotional full balance and ignoring the six month free amounts?
 

bill1024
If you add any purchases to the balance, you have to pay them off at 100% at the end of the month of that billing cycle, and still make the payment amount on the original purchase over and above what you added.
I have used one to buy a new guitar on payment with no interest, and I knew not to use that card for anything else until paid in full.
Been down that road long time ago with 0% teaser interest if you transfer a balance over.

Sorry I can be a little slow at times.   Are you saying that if I buy the card for 700 6months interest free, and then I buy a heap of misc stuff after that over the months that add up to 500,   my 5 payments of 100 only go toward the misc stuff and not the interest free 700? 

Credit company can be unpredicable about how payments are applied between promo balances and non-promo balances. Payments may be first applied to balances that are earning interest right away, and have charges that aren't (promo stuff) applied only if all non-promo stuff has been paid.
If it was the other way around, all the non-promo stuff would have already been racking up interest for the past few months, so you'll end up having to pay interest regardless unless you get your total balance down to zero.
 
You may want to look into Paypal's fine print to see how payments are applied to know exactly what's going to happen with payments.
 
also pay attention to if it's "Deferred" or "no interest" for 6 months, if it's deferred, on the 7th month you'll get interest for month 1-7, if it's no interest it's just for month 7. And it may not be clear which one it really is. (you'll want to look deeper into the terms to know for sure.)

Yeah, be careful... They do that. I had the same thing happen to me with Nebraska Furniture Mart. Bought a dishwasher a while back for around 600... Ended up getting some other things after that... Paid 1,000+ and because there was still a balance at the end of the 1 year term, it hit me for nearly 30% interest for the whole term. It added another 150-200 to my bill. There is a lot of this going around right now, so I don't opt for the promotion unless I know I can pay it off in less than half the time that's allowed, cause there is always shady stuff in the fine print.