Most fintech startups don’t set out to handle card data badly. The problem is that payment functionality often gets built quickly, security gets reviewed later, and “later” sometimes never arrives. By that point, data is being stored, logged, and transmitted in ways that would make an assessor wince.
There’s quite a lot to unpack here, so let’s look at where things tend to go wrong, and why these mistakes are more common than most teams realise.
Why PCI DSS Gets Overlooked in Early Builds
PCI DSS compliance is the framework that defines exactly what organisations can and can’t do with cardholder data. It covers everything from how data is stored to how it’s transmitted and who can access it. But early-stage startups often assume the standard only applies once they’re processing at scale, or that their payment processor handles it all.
That assumption can cause real damage. Even if you’re using a third-party gateway, there are still in-scope elements of your environment that need to meet the standard.
Storing CVV Codes After a Transaction
This one shows up more often than it should. A developer adds a field to capture the CVV during checkout and stores it in the database “just in case” it’s needed for retries or customer service queries.
CVV codes must never be stored after authorisation. This applies regardless of how the data is encrypted or where it lives. The standard is explicit on this point: post-authorisation storage of sensitive authentication data is prohibited, full stop.
The fix is simple: don’t store it. Pass it to your payment processor and discard it immediately. If your architecture makes that awkward, that’s a sign the architecture needs reviewing.
Full PANs in Debug Logs and Error Output
Logging is where a lot of card data exposure happens quietly. During development, it’s common to log full request and response payloads for debugging purposes. The trouble is that those logs often end up in production long after the original ticket is closed.
A full Primary Account Number (PAN) in a log file is a serious problem, particularly if your logs are centralised in a third-party tool or pushed to an external monitoring service. The standard requires that PANs be masked when displayed, showing only the first six and last four digits, and that they’re never stored in log files in unprotected form.
It’s worth auditing your logging pipeline periodically. Many teams find they’ve been capturing far more than they realised.
Card Data Sent Over Chat and Support Channels
This is largely a process failure instead of a technical one. Customers sometimes send card details over email, Slack, or a support ticketing system because they don’t know any better. If your team accepts and acts on that data without flagging it, you’ve just brought card data into an out-of-scope system.
Once that data lands in a support tool or chat log, it’s stored without encryption, visible to anyone with access to the channel, and potentially sitting there indefinitely. Staff training matters here. Your support team needs to know not to accept card data over unprotected channels, and to direct customers through secure alternatives.
Closing Thoughts
The card data mistakes that cause the most damage aren’t usually the dramatic ones. They’re the quiet, gradual kind: a logging setting that never got switched off, a database field no one questioned, a support process that never had a written policy.
Getting a handle on where your cardholder data lives, how it moves through your systems, and who can access it is the first step. From there, the requirements become a lot easier to meet.
