Every web2 payment flow I've ever shipped has the same shape: a request hits my server, my server calculates the amount and fees, and then my server updates the database. The fee only exists because my code enforces it. If someone finds a way around my API, say, using a direct database write, or a race condition, or even a webhook that never fires, then the fee just doesn't happen.
In Epoch 2 of #100DaysOfSolana, I built a token where this entire problem disappears. It disappears, not because I wrote better backend code, but because there was no backend to bypass.
The Web2 Way:
Fees Live in Application Code
Think about how a typical marketplace fee works. A buyer pays $100, your Stripe webhook fires, your server calculates a 5% platform fee, and your server moves $95 to the seller's payout and the $5 fee to your treasury. That logic lives entirely in your application layer. It is correct as long as nobody modifies to your database directly, nobody manipulates your webhook, and your cron job never double-fires.
