Payment

Agent Number accepts USDC over two payment rails: x402 (Coinbase-verified, Base) and MPP (Tempo). One year of unlimited SMS + voice for $1800 USDC.

Pricing

Item	Cost
One phone number, 1 year, unlimited SMS + voice	$1800 USDC
Check availability (`GET /availability`)	Free
Join waitlist (`POST /waitlist`)	Free
Pay via x402 or MPP	No surcharge
Per-message / per-minute	None during the subscription year

The 402 challenge

POST/subscribe with no payment header returns HTTP 402 with the x402 challenge body shown below. MPP is reachable on the same endpoint but discoverable separately at /.well-known/mpp.json — clients pick a rail and retry with the matching header (X-PAYMENT for x402, Authorization: Payment for MPP):

curl -X POST https://agentnumber.really.com/subscribe
# → 402
# {
#   "x402Version": 2,
#   "error": "X-PAYMENT header is required",
#   "accepts": [
#     {
#       "scheme": "exact",
#       "network": "base",
#       "amount": "1800000000",
#       "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
#       "payTo": "0x...",
#       "maxTimeoutSeconds": 300,
#       "extra": { "name": "USDC", "version": "2" }
#     }
#   ]
# }

Parse accepts[] to determine the active payment scheme + asset. Production settles in USDC on Base mainnet (x402) or pathUSD on Tempo mainnet (MPP). Don't hardcode — read from the live challenge or discovery file.

x402 (Coinbase-verified, Base)

x402 is a payment-required HTTP scheme. After parsing the challenge, sign a transferWithAuthorization message authorizing USDC transfer of amount from your wallet to payTo, then encode + retry:

curl -X POST https://agentnumber.really.com/subscribe \
  -H "X-PAYMENT: <base64-encoded-signed-payment>"
# → 200
# {
#   "token": "...",
#   "number": "+1...",
#   "expires_at": "2027-04-25T...",
#   "renewed": false
# }

The Coinbase x402 facilitator (x402.org) verifies the signed payment and settles on-chain. Your wallet doesn't need gas — settlement happens via meta-transaction.

MPP (Tempo) — pathUSD on Tempo mainnet

MPP is an alternative rail using Tempo's payment protocol. Same product, same price; different signing scheme. Build a Tempo charge credential with the mppx SDK and retry with Authorization: Payment instead of X-PAYMENT:

curl -X POST https://agentnumber.really.com/subscribe \
  -H "Authorization: Payment <base64-encoded-credential>"
# → 200 (same response shape as the x402 path)

Or use the npx mppx CLI to auto-handle the 402 → sign → retry end-to-end:

npx mppx https://agentnumber.really.com/subscribe --method POST
# one-time setup: npx mppx account create

OpenAPI advertises MPP support per-operation via x-payment-info per the mpp.dev discovery spec:

"x-payment-info": {
  "amount": "1800000000",
  "currency": "0x20c0000000000000000000000000000000000000",
  "description": "One persistent US mobile number, 1-year subscription (SMS + voice)",
  "intent": "charge",
  "method": "tempo"
}

Renewal

Re-paying with the same wallet renews the subscription and keeps the same phone number. The response field renewed: true indicates a renewal vs new issuance.

Common errors

Status	Meaning
`402`	Payment required — parse `accepts[]`, sign, retry with `X-PAYMENT` or `Authorization: Payment`
`402` on retry	Payment header malformed or signature invalid — verify amount + asset + payTo against the challenge
`503`	Number pool exhausted — check `/availability` + `/waitlist`
`500` w/ `facilitator_unavailable`	x402 / MPP facilitator returned an error — usually transient, retry

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