If you're trying to buy using a credit card or via paypal - sometimes the transaction becomes OFFLINE or PENDING.
Check your paypal account, what's your spending limit? In my account, see image below.
When you click on View Limits , this appears: SENDING Your Sending Limit has been removed. This allows me to buy anything as long as I have money in my Paypal or money available in my Credit card that's connected to paypal.
How about you? What's the status of your sending limit?
Do you want to remove it?