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:), withspl-tokenfor 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.
Test networks
The 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.
Related
This page is also available as Markdown: /docs/currencies.md. Questions: [email protected].