The common issues are usually caused by:
Wrong credit card details
Wrong CVV or CCV
Insufficient Funds
The card is expired
If those weren't the reason, many cases of denied payment happened because of the bank’s auto fraud prevention system. Since our company payment gateway is registered in Asia (Hong Kong) but you are ordering from US, Canada, UK, Australia, etc., it could easily get flagged as fraud.
This is unfortunately beyond our ability to solve the issue. The only recommendation we can give is to contact the card issuer to help authorize the purchase.