Deducting Store Credit (During Checkout)

Apply store credit to orders during POS checkout.

1. During POS checkout, select customer for the order
2. System displays customer's available store credit balance
3. Select "Store Credit" payment method or use in split payment
4. Enter amount to apply (defaults to full balance if sufficient)
5. System validates:
   • Customer has sufficient balance
   • Deduction amount doesn't exceed balance
   • Customer record exists and is valid
6. If valid, store credit is deducted locally
7. If Shopify integration active, balance is synced via debit mutation
8. Transaction history is updated
9. Remaining order total is displayed for additional payment

Balance Validation: System checks customer.storeCredit >== deduction amount before processing. If insufficient, warning is shown and transaction proceeds with remaining payment methods. Balance is checked both locally and (if possible) from Shopify before allowing deduction.