PHP Point of Sale (Open Source version) or InvoicePlane.
Look for POS systems built on Laravel or CodeIgniter . These are much easier to fix because they follow a strict structure (MVC), making it obvious where the "source code fix" needs to go. Conclusion php point of sale source code fix download
Troubleshooting and Optimizing Your PHP Point of Sale: A Guide to Source Code Fixes PHP Point of Sale (Open Source version) or InvoicePlane
Sanitize every price and quantity field. Users should not be able to enter text where a number belongs. php point of sale source code fix download
Are you dealing with a or a broken feature like the barcode scanner?