What a gas fee actually is
A public blockchain can only fit so many transactions into each block. When more people want to transact than there is room for, those transactions compete, and the gas fee is the price of that competition: it is paid to the validators or miners who produce blocks, in exchange for including your transaction in one. The name comes from Ethereum, where it is measured in units of "gas," but the same idea applies to every chain under different labels — a transfer always carries a network cost.
Two things drive the size of a gas fee. The first is how much work the transaction asks the network to do — a plain transfer is cheap, a complex smart-contract interaction costs more. The second is congestion: when the chain is busy, senders bid the fee up to get included sooner, and when it is quiet the fee falls. That is why the same transfer can cost very different amounts at different times of day, and why two chains carrying the same payment can charge wildly different fees.
The gas fee is paid in the network's own native coin, separate from whatever asset is being moved. Sending USDT on Ethereum costs ETH; sending it on Tron costs TRX; sending it on Solana costs SOL. So a wallet needs a small balance of the native coin to pay for a transfer at all, even when the thing being transferred is a stablecoin. The fee goes to the network, never to the sender's or recipient's counterparty.
What it means in a crypto payment
In a payment, the gas fee is the customer's cost of sending, and it shapes which network a payer prefers. A modest payment over a low-fee chain like Tron or Solana carries a network cost small enough to ignore, while the same payment on a congested chain can carry a fee that is meaningful against the amount being sent. That is much of why some networks have become the default rails for everyday stablecoin transfers: the fee does not eat into a small payment.
The gas fee also interacts with the difference between the amount a payer sends and the amount that arrives. When a customer pays the exact invoiced amount and the wallet deducts the gas fee on top, the full invoiced amount still lands. But a payer who is not careful — for example, asking a wallet to send their entire balance — can have the fee taken out of the amount sent, so that slightly less arrives than was billed. Understanding that the fee is a separate network cost helps explain why an occasional payment comes in a little short.
Gas fees on halfin
A gas fee is a property of the blockchain, not a halfin charge. When a customer pays an invoice, the network fee for their transfer is set by the chain they choose and paid by their wallet to that network — halfin neither sets it nor receives it. The amount halfin shows the payer to send is the invoiced amount; the gas fee sits on top of that, charged by the network the moment the transfer is broadcast.
Because invoices are anchored to fiat, the gas fee does not change the figure recorded in your ledger. You bill a fiat amount, halfin maps it to the payable amount in the chosen asset using the live rate and locks that figure when the invoice activates, and the customer's wallet pays the network fee separately. If a payer's wallet deducts the fee from the amount sent rather than adding it on top, the deposit can arrive slightly under the invoiced figure — halfin treats that as an underpaid invoice, surfaces it explicitly, and emits an invoice.underpaid event rather than silently marking it paid.
Gas fees also apply to money leaving the platform. When you send funds out through a single payout or a mass payout, that on-chain transfer carries the destination network's gas fee like any other transaction, because a payout is a real blockchain send. The fee is again a function of the chain and its congestion at the time, not a fixed halfin number.
- Set by the network — the chain and its congestion determine the fee, not halfin.
- Paid in the native coin — ETH on Ethereum, TRX on Tron, SOL on Solana, separate from the asset being moved.
- On top of the invoice — the payer sends the invoiced amount; the gas fee is the wallet's separate cost of broadcasting.
- Can cause an underpayment — a wallet that deducts the fee from the amount sent makes the deposit arrive short, which halfin flags as underpaid.