Issue #003 · Fintech Product Forge
Issue #001 was about what happens when a
payment fails.
Issue #002 was about what happens when a
payment runs late.
This week is about what happens before either
of those - when a bank tries to integrate with
your platform and gives up.
APIs are how FinTech products talk to the world.
Most teams treat them like plumbing.
The best teams treat them like products.
- Gaurav
🔩 THE FORGE
The integration failure nobody talks about
When a bank integration fails, the post-mortem
usually blames the bank.
Their developers didn't read the docs. Their
team didn't allocate enough time. Their
systems were too legacy to connect properly.
Rarely does the post-mortem ask the harder
question:
Was our API actually easy to integrate with?
In my experience - usually not.
Most payment APIs are built from the inside
out. Engineers design for how the system works
internally. The API reflects the internal data
model, the internal terminology, the internal
assumptions.
The bank's developers are then handed this
API and expected to figure out how it maps
to their world.
When they struggle, we call it an integration
problem.
It's actually a product problem.
What contract-first design actually means
Contract-first API design flips the process.
Instead of building the system and then
documenting the API - you define the API
contract first, before a single line of
backend code is written.
The contract specifies:
➥ Every endpoint and what it does
➥ Every request parameter and its type
➥ Every response field and its meaning
➥ Every error code and what caused it
➥ Every edge case and how it's handled
This contract becomes the agreement between
your platform and every bank that integrates
with it.
It sounds simple. The implications are
significant.
When the contract exists before the code,
your bank partners can review it, challenge
it, and flag problems before anyone has
written a single line of integration code.
A confusing field name costs nothing to
fix in a contract. It costs weeks to fix
after ten banks have already built against
the wrong assumption.
What versioning discipline actually prevents
The second half of the problem is versioning.
Most API teams add versioning reactively -
after the first breaking change causes an
outage, or after the first bank calls to
say their integration stopped working
overnight.
Versioning discipline means making a
commitment upfront:
We will never silently change the behaviour
of a published API version.
If behaviour needs to change - a new version
is created. The old version is supported for
a defined deprecation period. Banks are
notified with enough lead time to migrate.
Without this commitment, every API update
is a potential incident for every bank
that has integrated with your platform.
With it - banks can build with confidence.
They know what they're building against
will still be there next month.
What changed when we got this right
When we shifted to contract-first design
with structured versioning, three things
happened:
Integration success rate improved by 18%.
Banks that previously struggled to
complete integrations were completing them
faster and with fewer support escalations.
Support overhead dropped significantly.
The most common support tickets - "what
does this field mean", "why did this
response change", "how do I handle this
error" - reduced dramatically. The
contract answered those questions before
they were asked.
Trust improved. Banks started treating
our platform as a reliable dependency
instead of an unpredictable one. That
trust is hard to measure but easy to
feel - in renewal conversations, in
expansion deals, in referrals.
An API that banks trust is a competitive
advantage. In a market where every platform
claims reliability, the ones that
demonstrate it through their API design
stand apart.
The PM lesson
If you own a platform API - even partially
- ask yourself these questions:
Do your bank partners know what your API
will look like six months from now?
Do they know how you'll communicate
breaking changes before they happen?
Do they have a contract they can build
against with confidence?
If the answer to any of these is no -
your API is infrastructure pretending
to be a product.
The shift from API-as-plumbing to
API-as-product isn't a technical change.
It's a mindset change. And it starts
before the first endpoint is designed.
⚡ SIGNAL vs. NOISE
Open Banking APIs getting regulatory push | GraphQL adoption in FinTech is growing | AI-generated API documentation is here |
|---|---|---|
Regulators in the US and EU are pushing for standardised API formats for financial data sharing. For platform PMs, this is both a compliance requirement and a design opportunity. | More payment platforms are offering GraphQL alongside REST. The appeal is flexibility - banks can request exactly the data they need. | Several platforms are now using LLMs to auto-generate API docs from code. The output looks good. The accuracy is inconsistent. |
Standardisation reduces integration friction. It also reduces differentiation. Know which side of that tradeoff you're on. | The risk: flexibility without contracts is chaos. GraphQL without a schema discipline is worse than REST without versioning. | For regulated FinTech integrations, documentation that's almost right is worse than no documentation at all. Human review isn't optional yet. |
🧠 PM LENS
The API Product Checklist
Before your team publishes a new API or changes an existing one, run through
these:
BEFORE YOU BUILD | BEFORE YOU SHIP | AFTER YOU SHIP |
|---|---|---|
Is the contract defined and reviewed? | Does the implementation match the contract exactly? | What's your support ticket rate per integration? |
Have integration partners seen it? | Are breaking changes clearly flagged? | Which endpoints cause the most confusion? |
Are field names clear to an outsider? | Is the deprecation timeline communicated? | How long does a new integration take end to end? |
Are all error codes documented? | Do your docs show real examples? | Are you versioning proactively or reactively? |
Is the versioning strategy defined? | Has a non-engineer tried to integrate with this? |
🔗 ONE LINK WORTH YOUR TIME
Stripe's API design principles - publicly
documented and worth reading regardless
of whether you use Stripe.
Stripe built one of the most developer-
friendly APIs in financial services. Their
design decisions - predictable structure,
consistent error handling, versioning
discipline - are a masterclass in treating
an API as a product.
Not for copying. For understanding what
"API as product" looks like when it's
done well.
- Gaurav Nikumbh
Senior PM · Payments & Banking Infrastructure
Founder, TechVenture360
What's the worst API integration experience
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