The three most common reasons are:

Insufficient funds:
Make sure you have sufficient funds in your account.

The credit card is not issued from the country you are currently in:
The country issued must be the same as the country you are paying from.

Your bank blocks online payment for security reasons:
Contact your bank to check whether it blocks “international payments”.
If none of the above helps and you still receive the message “payment refused”, please proceed with PayPal.