What a token actually is
Every blockchain has a native currency: Bitcoin has BTC, Ethereum has ETH, Tron has TRX, Solana has SOL. That native coin is built into the chain itself and is used to pay transaction fees. A token is different — it is an asset layered on top of an existing chain rather than a chain of its own. It exists because the network lets people define additional assets through a standard, and the network records and moves them alongside its native coin.
A token standard is the agreed-upon set of rules that says how a token reports balances and how it is transferred, so any wallet or payment service can support it without bespoke work for each one. ERC-20 is the standard for fungible tokens on Ethereum; TRC-20 is its counterpart on Tron; SPL tokens are the equivalent on Solana. The mechanics differ between chains — on Ethereum and Tron each token is its own smart contract, while on Solana a single shared program manages every token — but the idea is the same: a common format that makes a token interoperable.
"Fungible" tokens are interchangeable, the way one dollar equals any other dollar; this is the kind that matters for payments. (Non-fungible tokens, NFTs, are a separate category where each unit is unique.) Because a token lives on a host chain, its transfers are recorded in that chain's blocks and moving it costs a network fee paid in the chain's native coin — sending an ERC-20 token consumes ETH, sending a TRC-20 token consumes TRX, and so on.
Token versus coin
The common shorthand is that a coin is a blockchain's own native asset, while a token is issued on top of an existing blockchain. BTC, ETH, SOL, and XRP are coins; USDT and USDC are tokens. The distinction is practical, not just pedantic: a coin pays the chain's fees and is part of how the chain works, whereas a token rides on the chain and pays its fees in the chain's coin.
One consequence is that the same token can exist on more than one chain. USDT is a token issued on Ethereum (as an ERC-20 token), on Tron (as a TRC-20 token), and on Solana (as an SPL token). These are the same dollar of value but different on-chain objects on different networks, each with its own fees and confirmation speed. Which standard a token follows depends on the chain the transfer was sent over, not just the token's name.
Tokens in a crypto payment
Most stablecoin payments are token payments. When a customer pays in USDT or USDC, they are sending a token issued on whichever chain they chose — an ERC-20 transfer on Ethereum, a TRC-20 transfer on Tron, or an SPL transfer on Solana. The receiving side identifies which token arrived from the transfer itself: on Ethereum and Tron by the contract address, on Solana by the mint address. That is what lets one receiving address accept several different tokens cleanly.
halfin runs gates for the specific tokens it supports — currently the USDT and USDC stablecoins across the chains where it has those gates, alongside each chain's native coin. A token payment is detected as a transfer to your receiving address and credited to the same fiat-anchored balance as any other asset, distinguished by its contract or mint address so USDT and USDC land in your ledger as the assets they are. halfin supports only the tokens it has gates for, not arbitrary tokens that happen to exist on a chain.
Because invoices are fiat-anchored, accepting a token does not ask you to reason about token mechanics. You bill a fiat amount; halfin maps it to the payable token figure using the live rate and locks that figure when the invoice activates, then shows the customer a concrete amount to send. Crediting is reorg-aware and waits for the host chain's confirmation threshold before the invoice is marked paid. A balance received as one token can later be paid out, refunded, or rebalanced into another asset through balance conversion — which is asset-to-asset, not a fiat withdrawal.