What a layer-2 is
A base chain — a layer-1, such as Ethereum or Bitcoin — secures every transaction directly through its own consensus, which makes it robust but also relatively slow and expensive once demand for block space rises. A layer-2 is a network that sits on top of a layer-1 to scale it: it executes transactions on its own, off the base chain, and then commits a compressed record of those transactions back down to the layer-1. The base chain stays the source of truth, while the day-to-day load moves up to the L2.
The dominant kind of L2 today is the rollup. A rollup batches many transactions together, executes them on the layer-2, and publishes the batch — along with the data or a proof needed to verify it — to the layer-1. Because the heavy work happens off the base chain and only a condensed result is posted on-chain, the per-transaction cost is a fraction of doing the same work directly on the layer-1. The L2 still leans on the layer-1 for its security: anyone can reconstruct or challenge the L2's state from the data posted to the base chain, so an L2 transaction is only as final as the base-chain settlement that backs it.
An L2 is not the same as a sidechain. A sidechain runs its own independent consensus and does not settle back to a base chain, so it carries its own separate security. A layer-2, by definition, derives its security from the layer-1 it settles to. That distinction matters when reasoning about how safe a payment is: on an L2, the guarantee ultimately traces back to the base chain.
Why it matters in a crypto payment
Fees are the immediate reason a layer-2 matters for payments. A stablecoin transfer on a busy layer-1 can cost more than the convenience is worth for a small purchase; the same transfer on an L2 built over that chain costs much less, because the network is designed to spread the base chain's cost across a whole batch of transactions. Lower fees make smaller crypto payments practical and leave more of the amount with the merchant rather than the network.
An L2 also tends to confirm transactions faster than its base chain, which shortens the wait between a customer paying and the payment being detected. The trade-off to keep in mind is that the same asset can live on several networks: USDC on Ethereum, USDC on Base, and USDC on Arbitrum are the same token standard but distinct deposits on distinct networks. A payment must be made on the exact network the address belongs to — sending funds for a layer-1 address out over an L2, or the reverse, is a mismatch, not a shortcut. Per-network confirmation rules and reorg behavior also still apply on each L2 individually.
Layer-2 support on halfin
halfin treats each supported layer-2 as its own settlement network rather than as a discount mode of Ethereum. Base and Arbitrum are Ethereum L2s that halfin supports alongside the layer-1, so a merchant can take a USDC payment on Base or an ETH payment on Arbitrum and have it settle on that network at L2 cost. Each network has its own deposit address and its own per-chain confirmation threshold, and crediting is reorg-aware on every chain, so an invoice is only marked paid once the deposit is deep enough to rely on.
Because the amount on an invoice is anchored to a fiat figure, the customer pays the same value whether they choose the layer-1 or a layer-2 — the network they pick changes the on-chain fee they pay and how quickly the deposit confirms, not what the merchant is owed. Offering an L2 alongside the base chain gives customers a cheaper, faster way to pay in the same asset, while halfin handles each network's settlement on its own terms.