diff --git a/src/collections/customers.ts b/src/collections/customers.ts
index ef729e8..6bb55f2 100644
--- a/src/collections/customers.ts
+++ b/src/collections/customers.ts
@@ -71,7 +71,7 @@ export function createCustomersCollection(slug: string = 'customers'): Collectio
             label: 'State/Province',
           },
           {
-            name: 'postal_code',
+            name: 'postalCode',
             type: 'text',
             label: 'Postal Code',
           },
diff --git a/src/collections/invoices.ts b/src/collections/invoices.ts
index d6412a7..8f57fc9 100644
--- a/src/collections/invoices.ts
+++ b/src/collections/invoices.ts
@@ -55,6 +55,7 @@ export function createInvoicesCollection(
         type: 'group',
         admin: {
           description: 'Customer billing information',
+          condition: customerCollectionSlug ? (data: InvoiceData) => !data.customer : undefined,
         },
         fields: [
           {
@@ -63,7 +64,7 @@ export function createInvoicesCollection(
             admin: {
               description: 'Customer name',
             },
-            required: true,
+            required: !customerCollectionSlug,
           },
           {
             name: 'email',
@@ -71,7 +72,7 @@ export function createInvoicesCollection(
             admin: {
               description: 'Customer email address',
             },
-            required: true,
+            required: !customerCollectionSlug,
           },
           {
             name: 'phone',
@@ -101,6 +102,7 @@ export function createInvoicesCollection(
         type: 'group',
         admin: {
           description: 'Billing address',
+          condition: customerCollectionSlug ? (data: InvoiceData) => !data.customer : undefined,
         },
         fields: [
           {
@@ -109,7 +111,7 @@ export function createInvoicesCollection(
             admin: {
               description: 'Address line 1',
             },
-            required: true,
+            required: !customerCollectionSlug,
           },
           {
             name: 'line2',
@@ -121,7 +123,7 @@ export function createInvoicesCollection(
           {
             name: 'city',
             type: 'text',
-            required: true,
+            required: !customerCollectionSlug,
           },
           {
             name: 'state',
@@ -136,7 +138,7 @@ export function createInvoicesCollection(
             admin: {
               description: 'Postal or ZIP code',
             },
-            required: true,
+            required: !customerCollectionSlug,
           },
           {
             name: 'country',
@@ -145,7 +147,7 @@ export function createInvoicesCollection(
               description: 'Country code (e.g., US, GB)',
             },
             maxLength: 2,
-            required: true,
+            required: !customerCollectionSlug,
           },
         ],
       },
@@ -329,6 +331,18 @@ export function createInvoicesCollection(
       ],
       beforeValidate: [
         ({ data }: CollectionBeforeValidateHook<InvoiceData>) => {
+          if (!data) return
+
+          // Validate customer data: either relationship or embedded info must be provided
+          if (customerCollectionSlug && !data.customer && (!data.customerInfo?.name || !data.customerInfo?.email)) {
+            throw new Error('Either select a customer or provide customer information')
+          }
+
+          // If no customer collection, ensure customer info is provided
+          if (!customerCollectionSlug && (!data.customerInfo?.name || !data.customerInfo?.email)) {
+            throw new Error('Customer name and email are required')
+          }
+
           if (data && data.items && Array.isArray(data.items)) {
             // Calculate totals for each line item
             data.items = data.items.map((item: InvoiceItemData) => ({
diff --git a/src/types/index.ts b/src/types/index.ts
index 9397668..64b22a1 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -140,7 +140,7 @@ export interface CustomerRecord {
     country?: string
     line1?: string
     line2?: string
-    postal_code?: string
+    postalCode?: string
     state?: string
   }
   createdAt: string
diff --git a/src/types/payload.ts b/src/types/payload.ts
index 8cd42ec..a4f2582 100644
--- a/src/types/payload.ts
+++ b/src/types/payload.ts
@@ -97,7 +97,7 @@ export interface CustomerData {
     country?: string
     line1?: string
     line2?: string
-    postal_code?: string
+    postalCode?: string
     state?: string
   }
   email?: string
@@ -142,15 +142,15 @@ export interface InvoiceDocument extends InvoiceData {
   amount: number
   createdAt: string
   currency: string
-  customer?: string // Now optional
-  customerInfo: {
+  customer?: string // Optional relationship
+  customerInfo?: { // Optional when customer relationship exists
     company?: string
     email: string
     name: string
     phone?: string
     taxId?: string
   }
-  billingAddress: {
+  billingAddress?: { // Optional when customer relationship exists
     city: string
     country: string
     line1: string