The integer pence rule: what compliance taught us about product
Three weeks before Seedr launched, our backend engineer flagged something that made no sense to me at first. Every transaction amount in our database had to be stored as an integer. No decimals. No floating-point calculations. Just whole pence. I pushed back. Surely we were overcomplicating things. But that one constraint reshaped how we think about Seedr, and it's why we're genuinely FCA-ready before we need to be.
A decimal is a time bomb
The problem, our engineer explained, wasn't mathematical. It was regulatory. If we ever want MRVL to hold money on behalf of creators and their audiences, the FCA will want an audit trail that's bulletproof. Every pence matters. Every calculation must be traceable, reproducible, and defensible under scrutiny.
Most fintech products don't start with this constraint. They start loose. They refactor later when compliance becomes urgent. By then, you've built schemas that assume floating-point arithmetic. You've scattered fee logic across three or four code files. You've got rounding errors that live in Excel macros.
We decided to do it backwards. Before Seedr ever charged anyone, we made the hard choice: integers only. £5.00 becomes 500 pence. A 5% platform fee becomes a calculated-then-stored integer, not a moving target. This meant every surface - the SDK, the creator profile at seedr.app/@handle, the dashboard - had to be designed around the same mathematical truth.
One source of truth, three surfaces
That decision cascaded outward. Our team centralised every fee calculation into one TypeScript file. Not one per service. Not one per SDK version. One. If a Foundr Pro creator's fee rate changes from 1% to 1.1%, it updates once, and every app that embeds the SeedrButton reflects it immediately.
The three surfaces - the Swift and Kotlin SDK (live in any MRVL app), the creator web profile, and the creator dashboard with Monday payouts - all hit the same Supabase backend. Same calculations. Same audit trail. When someone tips £5, the breakdown is always identical everywhere: 500 pence in, platform fee of 25 pence (or 7.50 for Foundr Free, or 5 for Foundr Pro), 475 pence reserved for the creator. Integer arithmetic. No surprises. No rounding ghosts.
It sounds tedious. It felt tedious in week two. By launch, it felt like clarity.
The AML threshold, written in pence
The integer discipline showed up again when we built in our anti-money laundering threshold. We set it at £10,000. Above that, a manual review happens. But in our code, it's 1,000,000 pence. A whole number. An FCA auditor could read supabase/functions/_shared/fees.ts and instantly understand the rule without wondering whether rounding might have created a loophole.
This matters more than it sounds. When regulators eventually review MRVL's Payment Institution application around 2028, they won't be hunting for clever product features. They'll be hunting for inconsistency, for arithmetic that doesn't track, for rules written one way in documentation and another way in code. Every integer we enforced now is a conversation we won't need to have then.
Why we didn't wait for permission
Seedr isn't FCA-authorised yet. We operate on Stripe Connect, which is. But we're already building as if we will be. Some founders might think that's paranoid. Others might call it premature.
I think it's honest. Our creators are real people - faith communities, church groups, comedians, makers - putting their work into MRVL apps and expecting to be paid cleanly. They deserve a platform that treats their money with the same rigour that a regulated institution would, even if we're not one yet. The integer pence rule isn't about impressing a regulator. It's about not pretending to be casual about something as serious as payment settlement.
That said, it also means when we do move toward Phase 3 of the MRVL Pay roadmap and seek Payment Institution status, we won't have a backlog of technical debt to rationalize. Our schema is already audit-ready. Our calculations are already traceable. Our source of truth is already singular.
What this taught us about product decisions
The integer pence rule is trivial on its surface. It's also revealing. It showed us that the best product decisions often come from the hardest constraints, not the loosest ones. A platform built around micro-tips (5 Seeds minimum, which is £5) needed to feel solid, trustworthy, and transparent. Hiding rounding errors behind decimal places would have done the opposite.
It also taught us that creators and their audiences don't care about your technical complexity. They care that the system works. That their £5 tip reaches the person they meant to support. That the math is the same everywhere. That a payout promised for Monday morning actually arrives on Monday morning.
Every app Seedr embeds into gets three lines of code: the SeedrButton. That simplicity exists because we made the hard choices first - not the easy ones.
If you're building something that touches money, especially within a creator community that deserves to be taken seriously, what constraints are you avoiding? And which ones might actually make your product better, not just more compliant.
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