01Follow the local behaviour
Card penetration, wallet adoption and cash-on-delivery expectations differ sharply between markets. Offering only what works in one country silently caps conversion in the others.
Look at attempted-payment data before assuming. The methods customers try and fail to use are the clearest signal you will get.
02Design for failure states
Declines, timeouts and abandoned authentication are normal traffic. Make retry easy, keep the basket intact and tell the customer plainly what happened.
Reconcile with the provider daily. Payments that succeed at the gateway but fail in your system are the worst kind of silent loss.
03Keep compliance boring
Use hosted fields or redirects so card data never touches your servers, and keep refunds, chargebacks and receipts auditable from day one.
Document who can issue a refund and log every one. This is a control question long before it is a technical one.