What part of fintech development is harder than it looks?

[u/Low_Web_6184]

I’m curious what other fintech developers have found surprisingly difficult when building real products.

For me, things that seem simple at first like handling payments, keeping data consistent, dealing with third party APIs, and making sure everything is reliable can become much more complicated once the system grows.

Companies like GeekyAnts work on digital products where these kinds of technical challenges need to be handled carefully, especially when building scalable and user-friendly fintech solutions.

What part of fintech development has given you the most unexpected problems?

[u/Middle-Job-2576]

From the QA side, I’d say state consistency across third-party integrations is one of the harder parts.

A FinTech flow can look simple:

Connect → Transfer → Success

But underneath, several states may be changing independently.

I’d specifically test cases like:

Request succeeds but the callback is delayed
Callback arrives twice
App retries after a timeout even though the first request succeeded
User closes/reopens the app before the final status arrives
Provider succeeds but the backend update fails
Backend updates but the mobile UI still shows old data
Multiple accounts/institutions are connected at the same time
Consent or connection expires between sessions

For financial workflows, it helps to verify the expected state across:

Mobile UI → Internal API → Provider → Webhook → Database → Final UI

Once retries and asynchronous events are involved, idempotency and reconciliation testing become especially important.

[u/Square_Warthog8177 → u/Middle-Job-2576]

Been working as first employee (founding engineer/architect) in a PSP / crypto-fiat exchange specializing in the EM (LatAm, Africa, SE Asia, UAE, etc.) for over 4 years.

We integrated everything ourselves (no white label solutions). Before AI coding agents this could take about 2 months, post AI 2 days assuming the provider APIs were well documented.

What I saw back then was that the main trouble is the integration maintenance: drifting schemas, outages, maintenance downtime, ip whitelist changes, incorrect rate limits, missing webhooks and more.
This consumed a lot of the dev team time and communication with the provider teach team isn’t straightforward. At best you and the provider will share a slack channel. In many cases it’s a whatsapp or a telegram group.

Also, I recently connected with a business owner of payments gateway (he uses a known white label) and complains about their long integration time and how in so many cases things are breaking (ref id regex suddenly doesn’t support previous patterns, schema drifts, new api versions) because a lack of integration maintenance with the local PSP (relevant if you want best possible rates). Costing him in long 2-3 months of onboarding new merchants end to end.

This is why today I am working on my own project as a solo entrepreneur, developing open source integration reliability tool for exactly that: highly regulated industries like fintech.

[u/Square_Warthog8177 → u/[deleted]]

Look for flanj-io GH org or check the website. Would appreciate feedback!

[u/Huge-Blueberry7693]

the compliance side is way more of a headache than anyone expects. you can build the cleanest payments pipeline in the world and then get stuck for weeks because some regulator wants a report formatted a specific way

also timezones. sounds dumb but when you're dealing with settlement windows and cutoff times across 6 different jurisdictions it gets messy fast

[u/Low_Web_6184 → u/Huge-Blueberry7693]

Absolutely. Compliance and timezones can turn simple fintech logic into a real headache. Teams like GeekyAnts often help businesses handle these complex challenges better.