Aryan Tuwar — Backend & Full-Stack Engineer. I build backends that don't lose money.

problem

Customers draw money from a credit line. A double-submit, a retry, or two concurrent requests could send the same money to the loan system twice — a real financial bug, not a cosmetic one.

approach

Built the feature end to end: 9 backend endpoints plus the customer UI. Guarded writes with idempotency keys and Postgres advisory locks, and split the money move into a two-phase finalize so the system always knows exactly what has already been sent downstream.

impact

Duplicate submits and race conditions can't move money twice. The finalize step is crash-safe — it never loses track of funds already sent to the loan system.

problem

Every credit-line activation submitted between 8pm and midnight Eastern was silently failing. Earlier in the day, everything worked.

approach

Traced it to a timezone mismatch: our servers ran on UTC, the vendor ran on Eastern. After 8pm ET, UTC rolls to the next calendar day — so the dates we sent no longer matched what the vendor expected.

impact

Fixed the date handling at the boundary. Late-evening activations — a meaningful slice of daily volume — stopped failing.

problem

No customer had autopay, which blocked the entire repayment feature set. Enabling it failed against the vendor with a vague 'malformed request' error that gave nothing to go on.

approach

Made autopay get created automatically when each credit line opens. Reproduced the failure directly against the vendor sandbox to pin down the real cause of the malformed-request error, then shipped the fix behind a feature flag.

impact

Repayments became possible for every customer — the foundation the self-serve cancel/edit payment features were then built on.

problem

When LoanPro was unavailable, the balance screen showed customers an error — exactly when they're most anxious about their money.

approach

Added graceful degradation: when live data isn't reachable, the screen falls back to the most recent archived snapshot instead of failing.

impact

Customers keep seeing their balance through vendor outages, with no hard error state.