Most bank cards and some credit card providers have certain restrictions. For starters, your card may not be setup to allow for international transactions to process. Most debit cards have a per day transaction dollar limit or per transaction dollar limit and/or may be subject to insufficient funds. Debit cards have more limitations / restrictions than credit cards. They are more likely to have a particular transaction flagged as fraud.
If you get a decline and do not call your bank, you will continue to receive a decline message. Declines do not suddenly get approved unless you call your bank. Before attempting another transaction please call the issuing bank or credit card provider so you have a better chance of having a successful transaction.