Show HN: Send21 – Crypto pay links an AI agent can create but can't spend

Send21 lets an AI agent or backend create a payment draft using a scoped API key that can create and track drafts but never spend, while a person always signs in their own wallet. The same flow is available over API or MCP (Streamable HTTP), and test networks on send21.io are for the demo only, with account drafts using live networks. A draft moves no money until someone signs it, so creating small drafts to your own address and canceling them is a safe integration test.