01
Cards
Payment gateway SDKs
A payment SDK is a product with exactly one user who never chose it:
the engineer integrating it under a deadline. The real problems aren't
cryptographic — they're integration time, binary size, and error
messages that say what actually went wrong instead of
ERR_UNKNOWN. Every ambiguous field in the docs becomes a
support ticket, then a failed payment, then a lost sale.
Working here taught me that developer experience is a
payments metric. The SDK's job is to disappear — to make the correct
integration the easy one, and the insecure one hard to write by
accident.
02
Rails
UPI
UPI is built on rails you don't own. As a third-party app (TPAP)
operating through a sponsor bank's PSP, you inherit a spec, a
switch, and a set of guarantees you can't change — and you build a
product on top that has to feel instant and forgiving anyway. The
plugin model is the whole challenge in miniature: your surface, the
network's semantics.
The lesson is about designing on borrowed ground —
where "it works on our side" isn't the bar, because the parts that
fail are the parts you don't control, and the user blames you either
way.
03
Authentication & certification
EMV 3DS and certification
3DS answers one question — is the cardholder who they say they are —
and shipping it under a certification body reshapes how you build.
The specification is the contract; conformance is graded by someone
outside your company; and "we'll fix it next sprint" isn't available
when the fix has to pass a test suite you don't administer. The
roadmap bends around approval windows, not just customer requests.
This is the part of the CV hardest to fake, and the
part I find most interesting. It's also the subject of
the interactive explainer — the honest way to
show protocol depth is to let you walk the protocol yourself.
04
Earlier — 2014–2020
Design and frontend
Before the platform work, there was the surface. Six years of design
and frontend engineering — interfaces, design systems, and the craft
of making a screen legible under pressure. I treat this as
foundation, not baggage: it's why I care what a payment
feels like, and why the 3DS explainer shows the cardholder's
screen next to the message flow.
A few pieces from that chapter, closed on purpose:
-
Coinome crypto exchange
Trading and wallet interfaces for a cryptocurrency exchange — the
most demanding thing I built in that period, and squarely on the
money-movement thread that runs through all of this.
-
Western Union remittance
Front-end work in the cross-border remittance space — money
moving between people and countries, the interface end of the same
problem I'd later work on from underneath.
-
Paymetry payments
A payments-adjacent product — an early turn toward the domain that
would become the whole career.
-
Design-system & interface work craft
A body of visual and frontend work from the period — kept as
evidence that the design half is real, not decoration.