Visa Flexible Credentials

Visa Flexible Credentials lets issuers wraps multiple payment credentials behind single primary credential that deploys across wallets, wearables and other non-card form factors, with banks consuming transaction decisions through the Visa Developer Portal. Transaction acknowledgement message consumption ran over TCP/IP socket connections carrying raw byte streams. Those sockets were unreliable and the system had a hard 5-second SLA from payment processing to acknowledgement. Target was to build system that supports 40M transactions a day.

Senior developer and the feature lead in a team of three backend engineers and one QA. Rebuilt the pipeline on Kafka, removing the socket failure mode entirely. Built custom observability on the Kafka Admin API with Prometheus and Grafana to show consumption behaviour per partition on kafka topic, then ran continuous performance testing against that dashboard to tune consumer configuration.

Acknowledgements for 40M transactions a day now run over Kafka rather than raw sockets, inside the 5-second SLA, with per-partition consumption visible while it happens.