Use the canonical host
Send paid requests only to https://machineinbox.com and verify the requirement's resource URL before signing.
X402 EMAIL API
Buy an inbox with USDC in the HTTP request.
Every unpaid request returns one HTTP 402 that advertises two rails: a PAYMENT-REQUIRED header with an x402 v2 requirement for USDC on Base mainnet, and a WWW-Authenticate: Payment challenge for Stripe MPP. Pay with either.
- Inbox
- $2.00
- Extension
- $1.00
- Settlement
- USDC on Base
- Protocol
- x402 v2
PAYMENT FLOW
A standard x402 v2 exchange.
- 01
Request
The agent POSTs to the paid route with an
Idempotency-Key. Machine Inbox returns HTTP 402 with a base64PAYMENT-REQUIREDheader describing an exact-scheme USDC payment on Base mainnet (eip155:8453). - 02
Sign
The x402 client signs the payment from its own wallet. Settlement runs through the PayAI facilitator; Machine Inbox never holds your keys.
- 03
Retry and activate
The client retries with one base64
PAYMENT-SIGNATUREheader and the same idempotency key. A successful response contains the inbox address and its bearer token.
BUYER CONTROLS
Keep payment and application retries bounded.
Pin the offer
Accept the requirement only when the amount is $2.00 for the seven-day inbox or $1.00 for an extension. Reject anything else.
Reuse the key
x402 requests require an idempotency key. Send a unique high-entropy value and reuse it for the paid retry and any recovery, so a retry can never buy twice.
RAILS
What each rail covers.
Replies are included with every paid inbox on both rails. Note that x402 settlement records on Base mainnet are public even after the mailbox is erased.
| Purchase | x402 (USDC on Base) | Stripe MPP |
|---|---|---|
| Seven-day inbox | $2.00 | $2.00 |
| Thirty-day pro inbox | Not offered | $5.00 |
| Seven-day extension | $1.00 | $1.00 |
| Authenticated replies | Included | Included |