Send crypto invoice payment links with send21 and track receipts by email

## Send crypto invoice pay links and mark payments with send21 For freelancers, agencies and small businesses that bill in their own currency, and for apps or AI agents that create invoices. send21: crypto pay links and API for people and AI agents. It is non-custodial: clients pay from their own wallet straight to your addresses. ### How it works 1. An n8n form, or a JSON POST from another app or AI agent, sends the invoice: client, email, amount, currency, optional invoice number. 2. The workflow creates a send21 pay link priced in that currency, payable in USDC or USDT on Solana, USDC or EURC on Base, or BTC over Lightning. 3. The link is emailed to the client and returned on the form page or as JSON. 4. A second branch receives send21 webhooks, verifies the V2 signature and updates the stored invoice. 5. Paid invoices send the client a receipt and you a note. Amount mismatches, expired links and unknown orders are emailed to you. ### Setup 1. Create a send21 API key at send21.io/api-keys with scopes drafts:write and webhooks:manage. Save it in n8n as a Bearer Auth credential on both send21 HTTP nodes. 2. Add an SMTP credential to the three email nodes. 3. In Set Your Addresses and Emails, add at least one receiving address you approved in the send21 app, plus your email and sender email. 4. Activate the workflow and follow section 8 to register the webhook. 5. Test: send a small invoice through the production form URL and pay the link. Requirements: a send21 account, an SMTP account and a public HTTPS n8n URL. ### Customization Add currencies to the form, edit the email texts, or store invoices in a database instead of static data. Questions: info@send21.io