The Revised Payment Service Directive (PSD2) aims to standardize APIs across EU banks, promoting open access to core banking functions like accounts and transactions. This directive introduces opportunities and risks for retail banks, with the Elastic Stack playing a crucial role in supporting the necessary API observability architectures. These architectures require robust logging, tracing, and metrics to monitor and analyze the system effectively, ensuring security, privacy, and quality of service. The Elastic Stack provides a comprehensive suite of products, including Beats, Logstash, Elasticsearch, Kibana, and X-Pack, to facilitate real-time data processing, machine learning, and alerting. By integrating these tools, banks can achieve enhanced scalability, maintain data observability, and improve operational efficiency, crucial for adapting to the competitive and evolving landscape introduced by PSD2.