Guide · Intermediate · 2026
When an agent wants to pay you but you have no 402
Someone (or some agent) is ready to send money. You have a wallet address. You do not have a paid endpoint that returns HTTP 402 with machine-readable requirements. That is the blind transfer problem.
What “blind” means
A transfer is blind when the payer cannot programmatically answer:
- How much is enough?
- Which asset and network?
- What resource unlocks after payment?
- How do I prove I paid so the server grants access?
- Can this proof be reused forever?
Humans paper over this with chats (“send 0.01 SOL and I’ll unlock it”). Agents cannot safely guess. They either overpay, underpay, pay the wrong chain, or refuse.
A live tip that almost worked
Picture an agent that wants to tip a tutorial site. It finds a public address in a footer. It can send SOL. It cannot know:
- whether the site will notice the transfer,
- whether a minimum amount exists,
- or how to get a receipt for its logs.
That is why educational projects that want agent tips expose a real /api/x402/… endpoint: the 402 body is the contract; the retry with proof is the handshake; the receipt is the audit trail.
Why x402 exists (in this light)
x402 turns “please pay me somehow” into a standard web response:
Request → 402 + accepts[] → pay → retry with proof → 200
The server publishes the price. The client does not invent a transfer memo and hope. Replay protection stops one payment from unlocking forever.
What to do if you only have an address today
- Publish a clear human page: network, asset, minimum, what the tip supports.
- Prefer Solana Pay QR / links for humans (amount + label + reference).
- For agents, add even a minimal x402 endpoint (this site’s donate flow is the pattern: on-chain verify + single-use proof).
- Log receipts. Agents and bookkeeping both need them.
Anti-patterns
- Posting a seed phrase or private key so an agent can “just pay.”
- Accepting any transfer of any size with no verification path.
- Unlocking content forever from one screenshot of a tx id.
Ship x402 is an independent educational project. Not financial advice.