Let your bank and credit card company that you will be using your ATM and credit cards in a foreign land to avoid denying of charges.
Unusual activity on a credit card or ATM card can raise enough suspicion to cause the issuer to deny the charge. Avoid this ahead of time by informing the card issuers that you will be traveling.
Review the information on the credit card’s website about using the credit card outside of the country. Here are links to the pages for Discover and American Express, but calling customer service is recommended prior to travel: