Developed a new extension capability for the Shopify/cli repository, focusing on enhancing payment extension integrations by introducing the Custom Onsite Payments Extension: Start Verification Session URL feature. This work involved adding an optional field to the extension schema, enabling extensions to specify a URL for initiating verification sessions. Leveraging TypeScript and JavaScript, the developer implemented schema validation and configuration mapping to support robust testing and deployment workflows. The changes streamlined verification flows, reduced manual intervention, and improved reliability across environments. Emphasis was placed on API design, extension development, and schema validation, resulting in improved developer experience and enhanced test coverage.