1)  Billing address field is sensitive, 97% of checkouts fail due to incorrect billing address registered to your debit / credit card bank on their file.

Example: If you moved from another state or have a past address and you have not called your bank to update your bank records, you'll need to type in your old billing address on page-1 and you'll type in the delivery address on page-2. They are different below is a video link demonstrating you how to do that visually. 

TGR-NOW.com How to check out successfully.

2) Another reason checkouts fail due to not meeting the minimum order amount that's required, during your checkout there will be an error status above the browser. Photo example below in green circle.