BizCore v3.0 Customer Credit & Invoice Control

INSTALL
1. Take full files and database backups.
2. Upload this ZIP to /public_html/ceylongemx.online/
3. Extract and overwrite.
4. Open https://ceylongemx.online/update-3.0.php
5. Click Install v3.0 Update.
6. Press Ctrl + F5.

FEATURES
- Line discount: none, fixed, percentage or per unit
- Invoice discount remains available after line discounts
- Customer credit limit enforced on projected outstanding
- Credit invoices require a customer
- Due date automatically uses customer/group credit days
- Live customer outstanding and credit information
- Customer groups: Retail, Wholesale, VIP, Dealer, etc.
- Salesperson assignment
- Live selected-warehouse stock availability
- Invoice cancellation with mandatory reason and stock reversal
- Customer statement and overdue control
- Payment receipt printing
- Daily sales and payment collection report

IMPORTANT
- Cancelling an invoice restores the remaining sold quantity only.
- Existing returned quantities are not restored twice.
- Cancelled invoices are excluded from active outstanding totals.
- Server-side stock, price, discount and credit validation remains authoritative.
