There are several reasons why a payment may decline. Some of the common factors include:

1. Insufficient funds in the account.
2. Transaction exceeding card limits.
3. Incorrect card details entered.
4. Expired or inactive payment method (e.g., credit/debit card).
5. Temporary account holds.
6. Fraud detection measures triggered.
7. Unsupported payment methods.
8. First-time online purchase.
9. Bank doesn't allow online transactions.
10. Different shipping and billing addresses.
11. Different IP address from card's issuing country.
12. Multiple transactions on one card in a short period.
13. Network or technical issues.
14. Payment gateway maintenance.

If your payment is declined, it is essential to double-check the provided information, verify account balances, and contact your bank or payment processor for more specific details about the decline reason.