My in-house CRM includes a POS billing module written in PHP that is miscalculating order totals right at checkout. Sub-totals, taxes, discounts and the final amount sometimes don’t add up, so customers see the wrong figure before they pay. Everything else in the system runs smoothly—only the arithmetic inside the checkout flow needs attention. I need a developer who can dive into the existing PHP codebase, trace the calculation logic, and correct whatever is causing the error. Once the fix is in place, I also want a quick sanity check on edge cases (multiple discounts, mixed tax rates, rounding) so the totals remain reliable under any normal scenario. Deliverables: • Updated PHP files (or clearly documented patch) that resolve the miscalculation • Brief summary of the root cause and steps taken • Confirmation, via a handful of test tickets, that totals match expected results across typical checkout scenarios If you are comfortable debugging PHP billing routines and can turn this around quickly, let’s get started.