How It Works

SellPolia is a set of on-chain contracts plus an off-chain indexer that watches them. The contracts hold funds and emit events; the indexer turns those events into a queue, matches buyers to sellers, and drives deliveries and payouts.

The lifecycle at a glance


SELLER                         SELLPOLIA                         BUYER
------                         ---------                         -----
deposit SETH  ─────────▶  SethVault (Sepolia)
                          emits SethReceived
                                 │
                          indexer creates a
                          FIFO queue order
                                                                 pays via
                                            PaymentCollector ◀── buy() / buyWithToken()
                                            emits SethPurchased   (payment chain)
                                 │
                          indexer matches the buy
                          against the queue (FIFO),
                          then the reserve backstop
                                 │
                          ├─ delivers SETH to buyer ──────────▶  SETH on Sepolia
                          │  (vault.sendSeth on Sepolia)
                          │
                          └─ seller accrues USD-owed
                                 │
                          daily Payout batch on Base
                                 │
paid in ETH  ◀─────────────  Payout (Base)

The three contracts

SethVault (Sepolia) — receives seller deposits (each becomes a queue order), holds the house reserve separately, and delivers sold SETH to buyers.
PaymentCollector (payment chains) — takes buyer payments in native coin or stablecoins, prices them on-chain via Chainlink, and emits the purchase event.
Payout (Base) — pays sellers in ETH, converting the USD they’re owed to ETH at the Chainlink ETH/USD price at payout time.

Two matching sources

Every buy is filled from two sources, in this order:

The live seller queue — open seller orders, oldest first (FIFO).
The SellPolia reserve — an owner-funded backstop inside the vault. When the queue can’t cover a buy, the remainder is filled from the reserve so buys never fail for lack of inventory.

Reserve liquidity is funded through a separate contract path (fundReserve()), so it never becomes a seller queue order and never competes with real sellers for payouts.

Read the details in Selling & the Queue and Buying & Fills.