fix(OUT-3617): AB-gate settings write path and backend validations

- Strip bankDepositFeeFlag/bankAccountRef from payload for non-AB portals
  (prevents garbage state if portal is later added to AB list)
- Reject bankDepositFeeFlag:true without bankAccountRef on the backend
- Fix res.Deposit.Id optional chaining inconsistency in payment.service.ts

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: SandipBajracharya

src/app/api/quickbooks/payment/payment.service.ts

@@ -262,7 +262,7 @@ export class PaymentService extends BaseService {
       await this.logSync(
         opts.paymentId,
         {
-          qbInvoiceId: res.Deposit.Id,
+          qbInvoiceId: res.Deposit?.Id,
           invoiceNumber: opts.invoiceNumber,
         },
         EventType.SUCCEEDED,

src/app/api/quickbooks/setting/setting.controller.ts

@@ -1,3 +1,4 @@
+import APIError from '@/app/api/core/exceptions/api'
 import authenticate from '@/app/api/core/utils/authenticate'
 import { SettingService } from '@/app/api/quickbooks/setting/setting.service'
 import { TokenService } from '@/app/api/quickbooks/token/token.service'
@@ -58,17 +59,31 @@ export async function updateSettings(req: NextRequest) {
   const parsedType = z.nativeEnum(SettingType).parse(type)
 
   const parsed = SettingRequestSchema.parse(body)
-  const { bankAccountRef, ...settingFields } = parsed
+  const { bankAccountRef, bankDepositFeeFlag, ...settingFields } = parsed
 
+  const isBankDepositAB =
+    parsedType === SettingType.INVOICE &&
+    isPortalInBankDepositABTest(user.workspaceId)
+
+  // Strip bank deposit fields for portals not in the AB test
   const payload = {
     ...settingFields,
+    ...(isBankDepositAB && { bankDepositFeeFlag }),
     ...(parsedType === SettingType.INVOICE
       ? { initialInvoiceSettingMap: true }
       : { initialProductSettingMap: true }),
   }
 
+  // Reject bankDepositFeeFlag:true without a bankAccountRef
+  if (isBankDepositAB && bankDepositFeeFlag && !bankAccountRef) {
+    throw new APIError(
+      httpStatus.BAD_REQUEST,
+      'bankAccountRef is required when bankDepositFeeFlag is enabled',
+    )
+  }
+
   const writeBankAccountRef =
-    parsedType === SettingType.INVOICE && typeof bankAccountRef !== 'undefined'
+    isBankDepositAB && typeof bankAccountRef !== 'undefined'
 
   // Wrap both writes in a transaction to prevent partial state
   // (e.g. bankDepositFeeFlag=true but bankAccountRef=null)