diff --git a/src/app/api/quickbooks/invoice/invoice.service.ts b/src/app/api/quickbooks/invoice/invoice.service.ts
index 889e8e5..b436d57 100644
--- a/src/app/api/quickbooks/invoice/invoice.service.ts
+++ b/src/app/api/quickbooks/invoice/invoice.service.ts
@@ -326,7 +326,7 @@ export class InvoiceService extends BaseService {
       syncLogConditions,
     )
 
-    return { ref: { value: qbItem.Id }, productDescription }
+    return { ref: { value: qbItem.Id }, productDescription, classRef: qbItem.ClassRef }
   }
 
   private async prepareLineItemPayload(
@@ -363,9 +363,9 @@ export class InvoiceService extends BaseService {
           // Doc reference: https://developer.intuit.com/app/developer/qbo/docs/workflows/manage-sales-tax-for-us-locales#specifying-sales-tax
           value: 'TAX',
         },
-        // classrRef is optional. ClassRef to reference the associated class of the QB item.
+        // ClassRef is optional. Only include when we have a value, otherwise QB will use the item's default class.
         // Doc reference: https://developer.intuit.com/app/developer/qbo/docs/api/accounting/all-entities/class
-        ClassRef: itemRef.classRef,
+        ...(itemRef.classRef && { ClassRef: itemRef.classRef }),
       },
       Description:
         typeof itemRef.productDescription === 'undefined'