# Currencies and networks

Payments settle in the asset the payer picks, directly to the receiver's own wallet. Prices can be set in any of 165 fiat currencies and convert at a rate locked for 15 minutes.

## What each network carries

| Network (API value) | Currencies (API values) |
| --- | --- |
| Bitcoin (`Mainnet`) | BTC (`Btc`) on-chain, and over Lightning with `paymentMethod: "Lightning"` |
| Solana (`Solana`) | `Usdc`, `Usdt`, `Eurc`, native `Sol`, wrapped BTC (`Btc`) |
| Ethereum (`Ethereum`) | `Usdc`, `Usdt`, `Eurc`, native `Eth`, WBTC (`Btc`) |
| Base (`Base`) | `Usdc`, `Eurc`, native `Eth` |
| Arbitrum (`Arbitrum`) | native `Usdc` (not USDC.e), native `Eth` |
| Polygon (`Polygon`) | native `Usdc` (not USDC.e) |

## Amounts and decimals

API amounts (`amountSats`, `amountBaseUnits`) are integers in the asset's base units.

| Asset | Decimals | Base unit |
| --- | --- | --- |
| BTC and wrapped BTC | 8 | satoshi |
| USDC, USDT, EURC | 6 | micro-unit |
| SOL | 9 | lamport |
| ETH | 9 | gwei (payment links carry the value in wei) |

## Payment links

- Bitcoin: BIP-21 (`bitcoin:`). Lightning: the invoice (`lightning:`).
- Solana: Solana Pay (`solana:`), with `spl-token` for tokens.
- EVM chains: EIP-681 (`ethereum:`) with chain id 1 (Ethereum), 8453 (Base), 42161 (Arbitrum) or 137 (Polygon).

## Detection and confirmation

- Payments are matched by exact amount at the receiver address. Use a fresh address per payment where you can.
- A transfer within 10% of the billed amount is flagged for the receiver to accept instead of being ignored.
- One confirmation by default; Polygon waits for 16. Solana counts finalized transactions.
- Native ETH is detected with free sources: public block explorers where they exist, optional free-tier explorer keys, and a balance check over public RPC.
- Lightning is confirmed through the receiver's Lightning address when the provider supports LUD-21. See [Lightning](https://send21.io/docs/lightning).

## Test networks

The [demo](https://send21.io/demo) covers Testnet4, Signet, Solana Devnet, Ethereum Sepolia, Base Sepolia, Arbitrum Sepolia and Polygon Amoy. On send21.io the test networks are reserved for the demo; account drafts use the live networks.

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Source: https://send21.io/docs/currencies