Developed TypeScript typings for the new issuingAddToWalletButton feature in the stripe/stripe-js repository, focusing on enhancing type safety and developer experience for API integration. The work involved defining comprehensive type definitions for configuration options and element types, ensuring that developers could integrate the wallet button with confidence and reduced risk of runtime errors. Usage tests were added to validate the typings and support robust integration workflows. By taking a typing-first approach using TypeScript and emphasizing API development best practices, the contribution streamlined the adoption of the Issuing Wallet flow and improved maintainability for teams working with stripe-js.