Chester Twomey developed support for the Caribbean Guilder (XCG) currency in the Shopify/money repository, enabling transactions in XCG by adding its ISO code, symbol, and formatting options. He approached this by updating the currency registry and formatting logic using YAML, ensuring the new currency surfaced consistently across both UI and API layers. Chester validated the end-to-end transaction flow, confirming accurate display and accounting for XCG in invoices, wallets, and reports. His work focused on precise currency configuration and data management, with no major bugs reported, reflecting careful implementation and attention to integration details during the one-month development period.