PayPal CREDIT is not a loan or a finance agreement it works the same way as a credit card so you can spend up to your credit limit, as far as I'm aware.
So for example lets say your credit limit is $1000 and you buy something for $900 your remaining available credit will be $100 and you can use it right away. However if you buy something for $1000 your remaining credit balance will be $0 so you have to pay some off to re-credit your balance.
