During January 2025, JT Berry focused on backend reliability for the getlago/lago-api repository, addressing error handling in billing workflows. He enhanced the PayInAdvance job by updating error propagation, specifically surfacing StaleObjectError to enable proper retry logic under high load. Previously, these errors were masked by generic rescue blocks, leading to failed fee generations. JT refactored the CreatePayInAdvanceChargeService to propagate these errors and introduced targeted tests to verify retry behavior and guard against regressions. Working primarily in Ruby, he applied backend development and testing skills to improve system resilience, though his contributions were limited to bug fixes during this period.