API Design
Look for clear request and response examples, stable order identifiers, meaningful errors, and a documented way to retrieve status. Test the actual endpoints you plan to use rather than relying on marketing claims.
The Importance of a Sandbox
Ask whether a sandbox is available and how test orders are separated from live payments. If a flow requires a real small-value test, document it and reconcile the receiving account afterward. Never simulate a paid status in production.
Clear Documentation
Without clear docs, integration is a nightmare. Look for gateways that provide copy-pasteable examples in NodeJS, Python, and PHP.
Questions about your own setup? Review the developer documentation or open your merchant dashboard.