4 October 2026 · 3 min read

Crypto payment gateway development for merchants

Invoices, confirmations, underpayments and settlement. A gateway is not an exchange, and the difference decides what you build and what you are liable for.

Payment work shows up in about one in seven crypto briefs, and it gets confused with exchange work constantly. A gateway takes money for something. An exchange trades one asset for another. The overlap is the chain layer and nothing else.

What a gateway actually does

1. A merchant requests an invoice for an amount in their currency.

2. You generate an address, lock a rate for a window, and show a payment page with a countdown.

3. A chain watcher sees the payment and counts confirmations.

4. You mark it paid, notify the merchant by webhook, and settle to them on a schedule.

Each of those four steps has an edge case that defines the product.

The edge cases are the product

• Underpayment. They sent 0.0098 instead of 0.01. Partial credit, refund, or hold? Decide and show the merchant the rule.
• Overpayment. Credit the excess, refund it, or keep a balance.
• Late payment. The rate window expired and the money arrived anyway. You are now holding funds at a price nobody agreed.
• Wrong chain. Someone sends a token on a network you did not expect. Recovery is manual and sometimes impossible, and the policy must be written before it happens.
• Reorgs. Same rule as an exchange: credit after confirmations, reverse if the chain reorganises.

A gateway is a set of policies with software attached. The code is the easy half; deciding what happens when money arrives wrong is the product.

Settlement decides your regulatory position

• Settle in crypto: you pass through what you received. Simplest, and the merchant carries the volatility.
• Settle in fiat: you now operate a conversion and a payout rail, which is a different business and usually a licensed one.
• Hold balances for merchants: you are custodial, with everything that implies in licensing terms.

Most trouble in this space comes from drifting into the second or third without deciding to.

What the merchant side needs

• An API with a plain invoice create call and a webhook with signature verification
• Idempotency, because webhooks retry and merchants double process
• A dashboard: invoices, their states, settlements and a downloadable statement
• Plugins only when there is demand, since each one is maintenance forever

What it costs

Quoted per project, because the chain count and the settlement choice dominate everything else. A single chain, crypto settled gateway with a merchant dashboard is close to a spot exchange build in effort. Fiat settlement turns it into a different conversation entirely.

Questions

What is the difference between a payment gateway and an exchange

A gateway accepts payment for goods and settles to a merchant. An exchange trades assets between users. They share a chain layer and almost nothing else.

How do crypto payment gateways handle price volatility

By locking a rate for a short window shown as a countdown. The hard part is the payment that arrives after the window closes, which needs a written policy rather than a case by case decision.

What happens if a customer underpays

Your policy decides: partial credit, refund, or hold until topped up. It must be defined up front and visible to the merchant, because it happens regularly.

Is a licence needed for a payment gateway

If you settle in fiat or hold merchant balances, very likely. Passing crypto straight through is a lighter position. As with exchanges, that is a lawyer's question in your jurisdiction.

How many confirmations before marking an invoice paid

Per chain and configurable, the same rule as exchange deposits. Fast chains can be credited sooner; the setting belongs in the console rather than the code.

Can you add a gateway to an existing exchange

Yes, and it reuses the custody layer and chain watchers. The new work is invoices, merchant accounts, webhooks and settlement.