--- title: "Usage-Based Billing for AI & API Products | Fynex" description: "Meter usage, price it seven ways, sell prepaid credits and cap spend. VAT invoices issue themselves, VAT shown in sterling, and reconcile to the payment." url: "/uk/features/usage-billing" --- Fynex is an AI-native finance operations platform — agentic finance — that automates and orchestrates end-to-end financial workflows for businesses. This page covers “Usage-Based Billing for AI & API Products” as part of the Fynex finance operation. Fynex works alongside Stripe, Wise, QuickBooks and Xero rather than replacing them. This page is relevant when a business wants invoicing, payments, payouts, reconciliation and cash run as one automated operation rather than staffed across several tools. # Your heaviest users should be your *best customers* Every request metered, priced and invoiced — so usage grows your margin, not your costs. *Usage-Based Billing.* ## A flat plan quietly loses money on the customers who use you most Every request your product serves costs you something — inference, compute, a third-party API. A flat plan is priced on the average user, so your heaviest customers turn into your least profitable ones, and you find out when the cloud bill lands. Moving to usage fixes the maths and breaks the billing: events have to be counted once, priced, and turned into an invoice nobody disputes. In a 2026 m3ter and PwC survey of 350 UK software executives, 44% struggled to capture usage data, revenue leakage ran at 4–7% of ARR, and 87% of billing systems weren't connected to the general ledger. The margin problem and the invoice problem are the same problem. ## From the first request to the payment booked Three steps from setup to settled — then it runs itself. 1. **Meter what costs you money** — Name a metric — API calls, tokens, seats, gigabytes — and send events by API, batch or CSV. A duplicate is dropped on its key, and a refused event waits in a queue to retry instead of vanishing from the invoice. 2. **Price it the way you sell** — Per unit, graduated, volume, tiered, package, percentage or per seat, with included units, a minimum and a spend cap. Try any price at any volume on the same engine that bills, before a customer ever sees it. 3. **The invoice issues itself** — At period close the usage is rated, the VAT invoice is numbered and sent with a payment link, and the payment is matched back to it — VAT on every line, the total in sterling, prepaid credit applied after VAT. ## Usage that turns into revenue you can see The four things a usage model breaks, and what happens to each. - **Every event reaches the invoice, once** — Each event carries its own key, so a retry never bills twice and a late event lands in the [right period](/glossary/metered-billing/). Anything refused — an unknown metric, an unmatched contract — is held with its reason for you to retry or discard. - **A new price without a new release** — A price is a dated version on the customer's contract. Change a tier from the first of next month and last month's invoices keep the price they were billed on — no migration, no ticket. - **Cash in before the cost goes out** — Sell credits up front and draw them down as customers use you. Top-ups, expiry and eight credit types — purchased, promotional, AI-token and more — sit on one ledger, and the unused balance exports as the liability your accountant asks for at year end. - **No bill shock, for them or for you** — Set a threshold and a cap per metric. Your customer hears at 80% instead of on the invoice, a hard cap stops usage where you agreed it would, and a spend cap stops the bill even when usage runs on. ## One customer's month, priced before it's billed A platform fee, 2.4 million API calls against a million included, VAT, and a prepaid credit applied after it — rated on the engine that bills, so the preview and the invoice agree to the penny. | | | |---|---| | Platform fee + API calls | £1,060 | | VAT at 20% | £212 | | Prepaid credit applied | −£200 | | Due · paid on the link | £1,072 | ## What it catches before the usage invoice goes out Fynex reads usage as it arrives and prices it as it goes, so a customer about to hit their cap, an event nobody can bill and a plan that costs more to serve than it earns surface in the month — not on the invoice, and not in the cloud bill. - Warns a customer before they cross their cap, not after - Holds events it can't bill — unknown metric, unmatched contract — for retry - Shows which customers cost more to serve than they pay - Flags the plan a heavy-usage cohort has outgrown - Recommends the price change, and never applies it without your approval ## The same job, with the leaks closed Point tools solve part of it. Fynex runs the whole thing on one platform. | The problem | Other platforms (A billing tool + a metering vendor) | Fynex | |---|---|---| | Count usage accurately | Build an event pipeline, or add a metering vendor on top. | Metering built in: one key per event, late events, a retry queue. | | Change a price | A new price object, a migration and a release. | A dated price version on the contract; history untouched. | | Sell prepaid credits | A wallet you build and reconcile yourself. | A credit ledger with top-ups, expiry and a liability export. | | Pay for the billing layer | 0.7% of billing volume (Stripe Billing), on top of processing. | No billing-layer fee on top: the card rate on what you collect, from 1.4%, covers it. | | Get paid, then pay out | Billing hands off to a processor; payouts are another vendor. | Invoice, payment, split payout and reconciliation on one record. | ## The rest of the job, also handled Beyond the headline job, every account gets the whole platform behind it. - **Per-seat pricing** — Seats rated from their history, prorated to the day. - **Test clock** — Run a year of renewals in the [sandbox](https://docs.fynex.ai/billing-api/v1/docs/sandbox) in a minute. - **Usage by CSV or webhook** — Send events from a warehouse export or a webhook — no code. - **Next-invoice preview** — Show a customer [what they will owe](https://docs.fynex.ai/billing-api/v1/docs/invoices) before the period closes. - **Signed webhooks** — Every invoice, credit and subscription state as an [event](https://docs.fynex.ai/billing-api/v1/docs/webhooks). - **Invoice to payout trail** — Each invoice traced to the payment and the [payouts](/features/payouts/) it funded. ## Your product, your books and your bank, kept in agreement Usage from your product or your warehouse, invoices out, payments matched back into your accounting system. 100+ integrations. **Accounting stack** — Every payment, fee and payout lands in your ledger, coded and reconciled — nobody re-keys it. QuickBooks, Xero, FreshBooks, Sage, NetSuite, Wave. **Banks & business accounts** — We read your balances and pay out of whichever account is cheapest — no bank portals, no copy-paste. Revolut, Wise, Mercury, Brex, Airwallex, Ramp. **Project & time tracking** — Hours, retainers and delivery status — so a project's real margin shows up without a spreadsheet. monday.com, Asana, Jira, ClickUp, Trello, Linear. **Site & app builders** — Whatever you built the business on — payments, invoicing and payouts wire into it without a dev project. Webflow, Framer, Lovable, Bubble, Softr, Glide. **CRM & sales** — The deal, the customer and the terms — pulled in so invoicing starts itself. HubSpot, Salesforce, Pipedrive, Zoho CRM, Close, Copper. **Payment acceptance** — Keep the checkout you already run. We take it from the moment the money lands. Stripe, PayPal, Adyen, Square, Braintree, Checkout.com. Your customers pay however they already pay — Visa, Mastercard, American Express, Apple Pay, Google Pay, Faster Payments, bank transfer and open banking — through the provider you run today or through us. ## Find what you're leaking, for free Send us your setup. We run a free diagnostic and show you what your payment stack costs you today. > One recent diagnostic found £2M in hidden fees across 10 processors for a proptech client. ## Questions, answered ### What is usage-based billing? [Usage-based billing](/glossary/usage-based-billing/) charges customers for what they actually consume — API calls, tokens, compute, seats or transactions — instead of one flat fee. Fynex meters the usage, prices it on your terms, issues the invoice at period close and matches the payment back to it, so the revenue follows the cost of serving each customer. For AI products specifically, see [billing for AI companies](/saas/ai-billing/). ### How does Fynex meter usage? You register a metric (sum, count, unique count, max, min or last value) and send events by API, in batches of up to 500, by CSV or by webhook. Each event carries an idempotency key, so retries never bill twice; refused events are held with a reason for you to retry or discard. The [usage guide](https://docs.fynex.ai/billing-api/v1/docs/usage-ingestion) documents every field. ### Which pricing models can I use? Seven: per unit, [graduated, volume](/glossary/graduated-vs-volume-pricing/), tiered, package, percentage and per seat — each with optional included units, a [minimum commitment](/glossary/minimum-commitment/) and a spend cap. Prices are dated versions on the customer's contract, and any configuration can be previewed at any volume on the same engine that bills. ### How do prepaid credits work? A customer buys [prepaid credit](/glossary/prepaid-credits/) up front; it is drawn down against their invoices as they're issued. Credit is applied after VAT — it pays the invoice rather than discounting it — so the VAT on the invoice stays correct. Eight credit types (purchased, promotional, AI-token, enterprise and more) share one ledger with expiry, and the unused balance exports as a liability for your accounts. More in [prepaid credits billing](/saas/prepaid-credits/). ### Are Fynex usage invoices valid VAT invoices? Yes. Each invoice carries HMRC's full VAT invoice fields — a gapless sequential number, time of supply, both parties, VAT category and rate per line — with the VAT total shown in sterling whatever currency you bill in. B2B customers in the EU get [reverse-charge](/glossary/reverse-charge/) wording enforced, and simplified invoices up to £250 are supported. ### How does Fynex compare with Stripe Billing, Orb or Metronome? Stripe Billing, Orb and Metronome meter and invoice; the payment, the payouts and the reconciliation live with a processor and other vendors — and Metronome is now part of Stripe, Orb part of Adyen. Fynex meters, invoices, collects, splits and reconciles on one record, beside the processor you keep. The full comparison is in [the best usage-based billing platforms](/compare/usage-based-billing-platforms/). ### Is there an API? Yes — the [Billing API](https://docs.fynex.ai/billing-api/v1/docs) covers metrics, events, prices, contracts, subscriptions, invoices and credits, with a sandbox and a test clock. Most teams configure prices from the dashboard and send events from their product; the API is there when you want billing driven by your own system. ## Bill for what they use. *Keep what you earn* --- The AI finance layer for platforms and operators. It runs the money chain and keeps more of it in your business. One platform instead of a dozen. 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