Sometimes there are paypal checkout issues.

First the order must have a USA payment source and a USA shipping address. If it does not then it is an international order.

 

If checkout is not working:

 
1. Try using a different PC or browser
2. Clear cache and cookies
3. If your checkout is a little grayed out, it usually means you may have some information missing.
4. Paypal is designed to work with Internet Explorer, but if you're using an older version of Internet Explorer, sometimes certain aspects of checkout won't display or function properly.
5. You can also try and check out using PayPal, not a credit card, to see if that helps.
6. Lastly, some of these tried-and-true fixes may resolve the problem: