When sending in payment you're directed to Paypal website where all transactions happen. In case an error message prompts please contact Paypal support immediately. It could be related to your Paypal account or shipping address. They are the ones who can provide better answer on how to successfully send in your payment. 

However, if you're brought to the same page or top part of the page, try to delete browser's cookies or check computer security software like Adblocker. This will sort it out.