What a blockchain is
A blockchain is a shared database with two defining properties: it is distributed and it is append-only. Distributed means there is no central server holding the authoritative copy — many independent nodes each store the full ledger and the network agrees on which version is canonical through a consensus mechanism. Append-only means transactions are only ever added, never edited or deleted in place; the history grows forward and earlier entries stay where they are.
The structure is what gives the chain its name. Transactions are batched into blocks, and each block carries the cryptographic hash of the block before it. That hash links the blocks into a sequence, so changing anything in an old block would change its hash and break every block that points back to it. To rewrite history, an attacker would have to redo the work behind that block and every block stacked on top of it faster than the rest of the network extends the honest chain — which becomes infeasible as more blocks accumulate.
Consensus is how a leaderless network agrees on one ordered history. Proof-of-work chains have participants expend computation to propose blocks; proof-of-stake chains have validators bonded with the network's own asset attest to them. Either way, the goal is the same: a single shared order of transactions that no one node dictates. The recent tip of the chain can still briefly fork — two valid blocks at the same height — and the network resolves the conflict by converging on one branch and discarding the other, which is a chain reorganization. That is why a transaction is not necessarily permanent the instant it lands in a block.
Why it matters in a crypto payment
A blockchain is the rail a crypto payment actually moves on. When a customer pays, they broadcast a transaction to the network; the network's nodes order it into a block, and the payment is recorded on the shared ledger that everyone can verify. There is no card network, acquirer, or correspondent bank in the path — the chain itself is the clearing and settlement layer, and the merchant's balance is whatever the ledger says it is.
This is also why a crypto payment is not final the moment it appears. The recent tip of a chain can reorganize, so a transaction that has only just been included can still drop back to unconfirmed. Each additional block built on top of it — each confirmation — makes a reversal exponentially less likely, until the transaction is deep enough to be treated as settled. Different blockchains reach that point at different speeds, because block times, reorg behavior, and finality guarantees vary from network to network. The same block depth on two chains does not represent the same strength of settlement.
Each supported blockchain is its own independent network with its own assets, address format, fee model, and confirmation behavior. A payment on one chain is invisible to another, so accepting a given asset means running against the specific chain it lives on — and a stablecoin like USDT or USDC can exist as a separate token on several chains at once.
Blockchains on halfin
halfin settles payments directly on-chain across several blockchains — Bitcoin, Ethereum and its ERC-20 tokens, the EVM layer-2 networks Base, Arbitrum and Polygon, BNB Smart Chain, Tron, the XRP Ledger, and Solana with its SPL tokens. Stablecoins are accepted as the chain-specific tokens they are: USDT on Tron, Ethereum and Solana; USDC on Ethereum, Base and Solana. A customer pays on whichever supported chain suits them, and the deposit is detected and credited on that chain.
Because every chain has its own settlement behavior, halfin applies a confirmation threshold tuned per network and credits reorg-aware. A deposit does not jump straight to paid: the invoice first reflects that a payment is confirming, then is marked paid once the transaction is deep enough on its chain to rely on. A deposit undone by a reorganization before it is final never leaves a paid invoice behind. The result is that the same invoice can settle at a different pace depending on which blockchain the customer paid on — a fast-finality network sooner, a chain that needs more blocks later — and webhooks follow that lifecycle so an integration can react to a payment confirming and then to it being paid.