fix: remove non-existent defaultCustomerInfoExtractor from README

Replace defaultCustomerInfoExtractor import and usage with a proper
working example that shows how to define a CustomerInfoExtractor function.

Co-authored-by: Bas <bvdaakster@users.noreply.github.com>

README.md

@@ -1,17 +1,19 @@
 # @xtr-dev/payload-billing
 
-A billing and payment provider plugin for PayloadCMS 3.x. Supports Stripe, Mollie, and local testing with comprehensive tracking.
+A billing and payment provider plugin for PayloadCMS 3.x. Supports Stripe, Mollie, and local testing with comprehensive tracking and flexible customer data management.
 
-⚠️ **Pre-release Warning**: This package is currently in active development (v0.0.x). Breaking changes may occur before v1.0.0. Not recommended for production use.
+⚠️ **Pre-release Warning**: This package is currently in active development (v0.1.x). Breaking changes may occur before v1.0.0. Not recommended for production use.
 
 ## Features
 
 - 💳 Multiple payment providers (Stripe, Mollie, Test)
-- 🧾 Invoice generation and management
+- 🧾 Invoice generation and management with embedded customer info
+- 👥 Flexible customer data management with relationship support
 - 📊 Complete payment tracking and history
 - 🪝 Secure webhook processing for all providers
 - 🧪 Built-in test provider for local development
 - 📱 Payment management in PayloadCMS admin
+- 🔄 Callback-based customer data syncing
 - 🔒 Full TypeScript support
 
 ## Installation
@@ -42,6 +44,8 @@ pnpm add @mollie/api-client
 
 ## Quick Start
 
+### Basic Configuration
+
 ```typescript
 import { buildConfig } from 'payload'
 import { billingPlugin, stripeProvider, mollieProvider } from '@xtr-dev/payload-billing'
@@ -70,6 +74,68 @@ export default buildConfig({
 })
 ```
 
+### With Customer Management
+
+```typescript
+import { billingPlugin, CustomerInfoExtractor } from '@xtr-dev/payload-billing'
+
+// Define how to extract customer info from your customer collection
+const customerExtractor: CustomerInfoExtractor = (customer) => ({
+  name: customer.name,
+  email: customer.email,
+  phone: customer.phone,
+  company: customer.company,
+  taxId: customer.taxId,
+  billingAddress: {
+    line1: customer.address.line1,
+    line2: customer.address.line2,
+    city: customer.address.city,
+    state: customer.address.state,
+    postalCode: customer.address.postalCode,
+    country: customer.address.country,
+  }
+})
+
+billingPlugin({
+  // ... providers
+  collections: {
+    payments: 'payments',
+    invoices: 'invoices',
+    refunds: 'refunds',
+  },
+  customerRelationSlug: 'customers', // Enable customer relationships
+  customerInfoExtractor: customerExtractor, // Auto-sync customer data
+})
+```
+
+### Custom Customer Data Extraction
+
+```typescript
+import { CustomerInfoExtractor } from '@xtr-dev/payload-billing'
+
+const customExtractor: CustomerInfoExtractor = (customer) => ({
+  name: customer.fullName,
+  email: customer.contactEmail,
+  phone: customer.phoneNumber,
+  company: customer.companyName,
+  taxId: customer.vatNumber,
+  billingAddress: {
+    line1: customer.billing.street,
+    line2: customer.billing.apartment,
+    city: customer.billing.city,
+    state: customer.billing.state,
+    postalCode: customer.billing.zip,
+    country: customer.billing.countryCode,
+  }
+})
+
+billingPlugin({
+  // ... other config
+  customerRelationSlug: 'clients',
+  customerInfoExtractor: customExtractor,
+})
+```
+
 ## Imports
 
 ```typescript
@@ -80,7 +146,17 @@ import { billingPlugin } from '@xtr-dev/payload-billing'
 import { stripeProvider, mollieProvider } from '@xtr-dev/payload-billing'
 
 // Types
-import type { PaymentProvider, Payment, Invoice, Refund } from '@xtr-dev/payload-billing'
+import type { 
+  PaymentProvider, 
+  Payment, 
+  Invoice, 
+  Refund,
+  BillingPluginConfig,
+  CustomerInfoExtractor,
+  MollieProviderConfig,
+  StripeProviderConfig,
+  ProviderData
+} from '@xtr-dev/payload-billing'
 ```
 
 ## Provider Types
@@ -99,9 +175,19 @@ Local development testing with configurable scenarios, automatic completion, deb
 The plugin adds these collections:
 
 - **payments** - Payment transactions with status and provider data
-- **invoices** - Invoice generation with line items and PDF support
+- **invoices** - Invoice generation with line items and embedded customer info
 - **refunds** - Refund tracking and management
 
+### Customer Data Management
+
+The plugin supports flexible customer data handling:
+
+1. **With Customer Relationship + Extractor**: Customer relationship required, customer info auto-populated and read-only, syncs automatically when customer changes
+
+2. **With Customer Relationship (no extractor)**: Customer relationship optional, customer info manually editable, either relationship OR customer info required
+
+3. **No Customer Collection**: Customer info fields always required and editable, no relationship field available
+
 ## Webhook Endpoints
 
 Automatic webhook endpoints are created for configured providers: