> ## Documentation Index
> Fetch the complete documentation index at: https://docs.momentco.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Quickstart: Customer Balance
> Accept a payment against a customer balance using the Billing API
This guide walks through the most common billing model: creating a customer with a balance and handling the payment webhook when that balance is settled. This model is suited for merchants who track a single running balance per customer without needing separate accounts or individual bills.
## Prerequisites
* A test API key. See [Authentication](/api-reference/getting-started/authentication).
* A registered webhook endpoint. See [Webhook Setup](/api-reference/webhooks/setup) to register your URL and obtain your signing key.
***
## Step 1: Create a customer
Create a customer with a `balance` representing what they currently owe, in minor units.
```bash theme={"system"}
curl -X POST https://api.momentpay.net/billing/customers \
-H "Authorization: Bearer sk_test_YOUR_SECRET_KEY" \
-H "Content-Type: application/json" \
-d '{
"external_reference": "UCR1234567890",
"name": "John Doe",
"email": "john.doe@example.com",
"currency": "ZAR",
"balance": 2000
}'
```
`balance` is specified in minor units. See [Monetary Amounts](/api-reference/getting-started/monetary_amounts) for details.
The response returns an `id`. Store this to reference the customer in future calls.
```json theme={"system"}
{
"id": "bcus_H4jp6KnU5cPw263v1jyz4",
"external_reference": "UCR1234567890",
"name": "John Doe",
"email": "john.doe@example.com",
"balance": 2000
}
```
***
## Step 2: Present the balance for payment
With the customer created, present their balance for payment using [Electronic Bill Presentment](/documentation/billing/ebp) or a [Payment Request](/documentation/collect/payment-links/payment-requests).
***
## Step 3: Handle the payment webhook
When payment is received against the customer balance, Moment sends an `obligation.amount_applied` event.
```json theme={"system"}
{
"id": "evt_2341234567890abcdef",
"type": "obligation.amount_applied",
"data": {
"id": "ob_N2a38DJQWPL8K4X42354234",
"amount": 2000,
"currency": "ZAR",
"payment_id": "pay_1313235234843nmafdsa",
"customer_id": "bcus_H4jp6KnU5cPw263v1jyz4"
}
}
```
Use `data.customer_id` to identify which customer paid and `data.amount` to reconcile against their balance.
Before processing, verify the event signature. See [Webhook Verification](/api-reference/webhooks/verification).
Respond with a `2xx` status code to acknowledge receipt.
***
## Next steps
Track balances across multiple sub-accounts within a customer.
Raise a specific bill with an amount due and a due date.
Present balances and bills to customers via a hosted payment page.
Ingest customer balances and bills in bulk via SFTP or file integration.
Examples for updating customer balances, account balances, and bills.