send21

send21 is non-custodial software that prepares payment instructions. Users create pay links or invoices priced in fiat (161 currencies) or as an exact crypto amount, either in the app or via a REST API or MCP server. Payers scan a QR code and pay from their own wallet; send21 never holds funds or private keys and watches the chain to notify the receiver by email and signed webhook when a payment is confirmed. The page states the send21 fee is never taken from the payment, and the receiver gets the full billed amount. Supported networks include Bitcoin (on-chain and Lightning), Solana, Ethereum, Base, Arbitrum and Polygon. The site also offers scoped API keys, idempotent draft creation, batch drafts (up to 25), recurring payments, and a testnet demo.

Key features

• Pay links and invoices priced in fiat currencies (161 currencies) or exact crypto amounts
• Non-custodial: payments go directly from payer to receiver wallet
• Supported currencies: BTC (on-chain and Lightning), USDC, USDT, EURC, SOL, ETH, WBTC
• Supported networks: Bitcoin, Lightning, Solana, Ethereum, Base, Arbitrum, Polygon
• REST API for creating drafts and pay links (POST /payment-requests, POST /api/v1/drafts)
• MCP server for AI agents at https://send21.io/mcp
• Scoped API keys (drafts:write, drafts:read, webhooks:manage)
• HMAC-SHA256 signed webhooks such as draft.confirmed
• Idempotency-Key support for safe retries and batch creation of up to 25 drafts per call
• Recurring daily, weekly or monthly drafts
• Exchange rate locked for 15 minutes and recorded on the payment
• Transaction template endpoint for signing with your own node or wallet
• Payment status endpoint with txid and confirmations

Best suited for

• Individuals and businesses wanting to accept crypto payments via pay links or invoices
• Webshops and merchants taking crypto online and at the counter
• AI agents that create payment requests while a human or operator wallet signs payments
• Developers integrating crypto payments through an API or MCP

Pricing

One fee per payment, tiered by size: 0.49% on small payments down to 0.01% above $100,000, with a $0.01 minimum and $100 maximum. Free account with no subscription or setup fee.