n8n Send21 Crypto Invoice Payments: Email Pay Links

Get paid in stablecoins or Bitcoin—automatically—by sending Send21 crypto payment links from n8n

This n8n workflow turns your invoice details (client, email, amount, currency) into a Send21 pay link, emails it to your client, and then marks the invoice paid only after Send21 confirms payment via a signed webhook. No manual chasing, no holding funds—your client pays from their own wallet.

What this workflow does

• Collect invoice input: An n8n form or JSON webhook provides client, email, amount, and currency.
• Create a Send21 payment link: The workflow generates a Send21 pay link using USDC/USDT on Solana, USDC/EURC on Base, or BTC over Lightning. The invoice number is the order id, and an idempotency key ensures retries return the same link.
• Email the pay link: Your client receives the payment link via email.
• Verify payment securely: When paid, Send21 sends a signed webhook. The workflow uses n8n’s Crypto node to validate the V2 signature over the raw body, rejects deliveries older than 5 minutes, ignores repeated delivery ids, and matches order, amount, and currency.
• Update invoice status: The invoice is marked paid and a receipt is emailed. Payments with a different amount are flagged and never accepted on their own.

Use cases

• Freelancers and agencies sending crypto invoices in EUR, USD, or other supported currencies
• SaaS operators automating “invoice paid” status without manual reconciliation
• Teams that want customers to pay from their own wallet while Send21 handles the crypto transfer

Technical details

• n8n nodes / logic: if, set, code, form, crypto, switch
• External services: Send21 API + SMTP (for emailing pay links and receipts)
• Security: Bearer Auth for Send21 API key, webhook secret stored in a Crypto credential, signature validation with raw-body V2 signature checks
• Setup steps: Add credentials, enter approved receiving addresses in the Settings node, run Register webhook (run once), and store the returned secret