Step-by-Step Guide to Implementing Credit-Based Billing

Step 1: Define Your Credit Unit and Rate Card

Firstly you should define what a credit denotes. For instance, 1,000 tokens burn 1 credit or it takes 10 credits to process one image. Then you should build a credit rate card that includes your compute cost plus a healthy margin.

Step 2: Build the Wallet and Ledger System

Create a wallet table for every customer, along with append-only ledgers that show every credit, debit and expiration. Your system should run on atomic operations ensuring a credit transaction is completely recorded or not recorded at all.

This helps you make sure there are no partial records that could lead to lost or double-charged credits.

Optimistic locking is another way you can keep your data safe and accurate. Here your system allows multiple people or processors access and update the data but all of the data is reconciled before taking any further actions.

If another process has already updated the data, the system will reject the current update, preventing overwrites and ensuring data consistency.

Having idempotency keys for every transaction helps in billing duplicate charges. Idempotency keys are unique identifiers attached to each transaction. If the same request is sent multiple times, the system recognizes the idempotency key and processes the request only once.

Step 3: Set Up Metering and Usage Tracking

Every API call made and every GPU second used is a billable event and tracking every event with utmost accuracy is very important.

Your system should be able to track these events in real-time without letting any one of them slip through.

Your rating logic then translates these events into the number of credits used up. Flexprice uses Kafka and Clickhouse which make AI usage tracking and aggregation simple and effective.

Step 4: Implement Live Enforcement

Like you check your bank balance before buying something, your system should check if the customer has enough credits before starting with the AI inference.

Hold some credits for long running tasks like processing a batch of images. Your system should be capable of auto top-ups and sending alerts in case of low balance.

This kind of system is more thoughtful and efficient rather than running out of credits during critical computes and doing everything manually.

Step 5: Add Transparency and Reporting

It is never enough talk when it comes to billing transparency. More than being honest with your customers, you are protecting your brand equity as well.

Provide API endpoints to fetch wallet and ledger data along with running daily reconciliation jobs to catch and resolve any revenue leakage. When your customers can see their usage patterns, available balance and expiry rules all in real-time, you build a bridge of trust with them.

You are not just making money for yourself but you are building a brand that your customers can blindly rely upon.

Step 6: Establish Expiration, Rollover, and Refund Policies

Every reward comes with an expiry date. You either use it in time or it's lost. You should define these expiry dates for the credits.

On an enterprise level, you can let the credits rollover for the next billing period so that your customers are not panicking over unused credits.

For when there are any refunds that need to be made in cases where your customer cancelled a plan, your system should support workflows in order to do them smoothly. And if you are giving your customers any promotional credits, you might want to set different rules like early expiry or no rollovers.

This is a fool proof way to keep your billing system fair, transparent, and easy to use, no matter what kind of customer you are serving.

Best Practices for Scalable Credit-Based Billing

• Use Append-only Ledgers for Auditability

Your ledger should contain all the data starting from every usage, credit, debit, and expiry in an incremental manner so that no data gets erased and keeping track of changes and auditing get simpler.

• Maintain Real-Time Balances with Cache Invalidation via Event Streams

You should follow the practice of keeping customer balances up to date by using event streams to instantly refresh cached data. When a credit is used up or added, your system knows right away and users always see the latest information.

• Deduplicate Usage Events Using Idempotency Keys

If a request gets sent twice might be because of a network error or system reboot, idempotency keys make sure it is counted only once. This ensures your billing is accurate and double-charging doesn't take place.

• Keep Pricing Configs Externalized

Always store your pricing rules outside your code as a separate chunk, so that you can tweak rates or add new plans without redeploying your entire system.

This is exactly why Flexprice is easier to integrate with your existing systems and make billing scalable without needing to write your code all over again.

Set Up your Credit Based Billing with Flexprice

Credit systems are notoriously hard to build in-house. You need real-time balance checks, accurate debits, wallet consistency, expiration logic, top-ups, previews, entitlements, and fail-safes that don’t break under load.

Flexprice ships all of this out of the box so you can launch a production-ready credit model without writing custom billing code.

Flexprice gives every customer a dedicated credit wallet that updates in real time as events are ingested.

Each wallet supports prepaid credits, pay-as-you-go debits, bundled allowances, expirations, and package renewals, letting you design any credit system from simple prepaid bundles to complex hybrid pricing with multiple meters.

You define how credits should be consumed using usage meters, and Flexprice automatically ties every event to your pricing logic.

Credits are deducted atomically so balances remain accurate even when you’re handling millions of events per second. No race conditions. No double-spends. No manual reconciliation.

Finance and engineering teams get full transparency with real-time balance visibility, credit usage summaries, consumption audits, and per-customer pricing overrides.

You can even simulate consumption using usage previews before committing changes, a powerful tool when adjusting plan rules.

Flexprice’s credit system also plugs directly into invoicing, entitlements, and reporting, so customers see exactly how their credits were consumed and what they’re paying for.

And because Flexprice is open-source and self-hostable, you can scale credit logic inside your own VPC with full control over data retention, compliance, and performance.

What you Can Ship in Days With Flexprice

• Prepaid Credit Bundles: Sell credit packs, auto-top-ups, and recurring allowances.

• Multiple Credit Meters: Track and deduct different types of usage from one wallet.

• Atomic Credit Deduction: Guaranteed accuracy even at high ingestion volumes.

• Credit Expiration & Renewals: Configure lifespan, carryover rules, and auto-refills.

• Usage Previews Before Billing Updates: Validate pricing before publishing customer-facing changes.

• Full Auditability: Every credit debit, expiry, top-up, and event is logged.

• Self-Hosted Deployment: Run the entire credit system inside your VPC with no lock-in.

If your product needs a reliable, scalable credit-based billing engine, Flexprice lets you launch one in a few days instead of spending months rewriting billing logic every time your pricing evolves.

Frequently Asked Questions(FAQs)

1. How should we design credits so billing stays transparent and fair?

Start by defining a clear credit unit that maps directly to compute, and keep your rate card public and versioned so pricing stays transparent. Track everything in a wallet backed by an append‑only ledger, and make sure every deduction happens atomically with an idempotency key to prevent double counting. Show users their live balance and expiry details, send low‑balance alerts before interruptions.

2. How do we prevent double-spends and concurrency errors in credit wallets?

Give each usage event an idempotency key. Use atomic deductions with optimistic locking or serializable transactions. For long tasks, use a hold-and-settle flow. Retries collapse to one write, concurrent updates retry cleanly, and late events are handled through separate auditable corrections.