Pay-per-request with x402 or a monthly plan: how to bill an API in stablecoins.

What is x402?

x402 is an open standard for paying for a web resource inside the HTTP request itself: the server replies 402 Payment Required with a price, and the client pays and retries. x402.org describes it as "an open, neutral standard for internet-native payments" and says it "supports all EVM-compatible chains, Solana, and more", with stablecoins as the main use. Fianto publishes this post and sells subscription billing, not x402; we have no stake in the protocol and do not implement it.

The README of the x402 Foundation's reference implementation on GitHub lays out the flow:

1. The client calls an endpoint on the resource server.
2. The server answers 402 Payment Required, with the accepted payment options in a PAYMENT-REQUIRED header.
3. The client picks one, signs a payment and repeats the request with a PAYMENT-SIGNATURE header.
4. The server checks the payment itself or posts it to a facilitator's /verify endpoint, then settles it on chain directly or through the facilitator's /settle endpoint.
5. The server returns 200 OK with the resource and a PAYMENT-RESPONSE header.

The README defines a facilitator as "A server that facilitates verification and execution of payments for one or many networks." Its exact scheme transfers a specific amount, such as $1 to read an article. Source: x402-foundation/x402 on GitHub, which took over from the original coinbase/x402 repository.

How does x402 run on Solana, and what does it cost?

On Solana, Coinbase's facilitator supports SPL tokens with the exact and upto schemes, according to its CDP Facilitator page on 15 October 2026. The same page lists its pricing: up to 1,000 on-chain transactions a month free, then $0.001 each. It adds: "Facilitator fees are based on onchain activity, not payment requests. Payment verification is always free." An exact payment settles in one on-chain transaction, while Solana upto uses two (an escrow deposit and a settlement). Its batch-settlement scheme, which claims many payments in one transaction, is listed for EVM networks such as Base, not for Solana.

Usage is measurable. On 15 October 2026 x402.org showed, for the last 30 days, 75.41 million transactions and $24.24 million in volume, an average of about 32 cents a transaction by our division. Coinbase's x402 docs say CDP "has processed more than 100 million x402 payments across Base and Solana."

x402.org says the protocol is "free for the customer and the merchant", leaving the network fee. A facilitator is a separate service with its own price, as the Coinbase table shows, and a Solana transaction pays a base fee of 5,000 lamports per signature under Solana's fee rules.

How does a capped monthly plan bill an API instead?

A capped monthly plan charges one fixed price per period from the customer's wallet, after the customer approves it once with a cap per period. With Fianto the customer signs one Solana transaction at checkout that pays the first period; after that, Fianto collects each renewal through the Solana Foundation's Subscriptions program, which refuses any charge above the cap or to a wallet the plan does not name. How that works in detail is on the Solana subscriptions page.

• Intervals: monthly means every 30 days and yearly every 365 days. There is no per-request, metered or weekly billing.
• Prices: 0.01 to 1,000,000 USDC, so a single Fianto payment cannot be smaller than one cent; pricing in USDC covers the limits and the fees on top.
• Who pays: you pay nothing. The customer pays a flat 0.01 USDC network fee with each charge today, the Solana fee for the checkout transaction (under $0.01), and account rent in SOL, about 0.00144 SOL as of 15 October 2026 for the subscription account, which comes back when they reclaim it after the subscription ends. A first subscription from a wallet also pays about 0.00119 SOL, not returned, for a one-time wallet setup. The checkout shows the live amounts.
• Fianto fee: none during the beta; after it, about 0.1 to 0.5% on top, paid by the customer.
• Failed renewals: the subscription goes past due and Fianto tries four times in all, at the period boundary and then about one hour, six hours and a day after it, before ending it.

Which costs less at 30,000 requests a month?

At 30,000 requests a month priced at $0.002 each, a customer paying per request through Coinbase's facilitator generates 29,000 billable settlements, $29.00 in facilitator fees on $60.00 of revenue, if every request settles as its own payment. The same customer on a 60.00 USDC monthly plan makes one charge a month.

The last row is the real trade-off. Per-request pricing tracks use exactly, which a light user likes and your revenue forecast does not. A monthly plan charges the light user for capacity they never touched. The fee row depends on choices you control: you can run your own facilitator and settle on chain yourself, and the Coinbase prices may change, so treat the $29.00 as one dated example, not a rule.

When is per-request payment the better choice?

Per-request payment wins when the caller has no account with you and may never come back. An AI agent buying one dataset lookup, a script that hits your endpoint twice a month, a public API that wants no sign-up page: for these, x402's model of paying inside the request removes the account, the API key and the checkout. Coinbase's docs put it plainly: "There is no checkout page, card form, or signup flow."

A monthly plan wins when the same customer calls every day, when you want revenue you can forecast, and when your customer wants a fixed line on their own budget. It also keeps the customer's signatures to one: after checkout, renewals need nothing from them. Fianto fits only this second case. If your API needs per-call pricing, use x402 or another usage-based tool, not Fianto.

Where do Solana allowances fit between the two?

An allowance is a pre-approved spending budget: the customer lets a provider draw up to a cap, and the provider takes payments within it as usage happens. Solana's announcement of Subscriptions and Allowances says: "Allowances (Fixed Delegation) let a user pre-authorize a one-time spend up to a defined cap, with an optional expiration." It names two other models in the same program: Recurring Delegations, where the cap resets each cycle, and Subscription Plans, fixed billing tiers a merchant publishes on chain.

That is a middle path between x402 and a flat plan: usage-based pulls under a cap the customer set in advance. Fianto's plans use the per-period caps of the Subscriptions program, and Fianto offers no allowance or usage-based product today, so an API that wants capped pay-as-you-go billing would build it on Solana's allowances itself.

How to sell a monthly API plan for USDC with Fianto

1. Create the product with a monthly price in the dashboard, once your merchant account is approved.
2. From your server, create a checkout session in subscription mode for that price, and send the customer to the hosted checkout.
3. Grant the API key on subscription.created, keep it on subscription.renewed, warn the customer on subscription.past_due and revoke the key on subscription.ended. A subscription creates no order, so order.paid never fires for it.

The plan design for API and RPC products, with tiers and key handling, is in accepting USDC for API plans, and the event-to-access mapping is in granting access from webhooks, with a worked Express version in USDC subscriptions in Express. An AI coding agent can write those webhook routes for you with the Fianto agent skill. Each event is described in the docs under event types.