So let say you have a bunch of gift card or rebate card where it has certain value such as $10 $20 $100, and so you purchased items the balance decreased and you end up with $1.67 for example and you try to buy something that cost 99 cent but your card got declined, you know why? because most likely your card was pre-auth with $1 so now making your card only have 67 cent left. So what I found out was for Visa pay via paypal no pre-auth taken place, only with American express

paypal pre-auth $1 preauth on American express credit card but doesn’t on visa credit card