Worked on enhancing the centrapay/documentation repository by implementing idempotency in the Payment API to improve reliability and developer experience. Introduced an idempotencyKey field to the pay-a-payment request API using JavaScript, which prevents duplicate transactions across payment flows. Updated snapshot tests to ensure the new idempotency behavior was accurately reflected and validated end-to-end compatibility with existing systems. Comprehensive documentation was created in Markdown to guide integrators on the correct usage of the idempotency feature. This work focused on robust API development and clear documentation, reducing the risk of duplicate charges and supporting more predictable payment processing for developers.