Backend Accounting Module Integration

Our custom backend already powers the website and POS. I now need the accounting layer added so day-to-day numbers flow straight from sales to books without manual transfer.

Core features I want live in this first phase:
• Expense tracking that pulls cost data directly from existing records.
• Financial reporting dashboards for P&L, balance sheet and cash-flow snapshots.
• A complete general ledger with accounts payable, accounts receivable and automated bank-reconciliation tools.

Everything must post correctly to trial-balance level so that I can export tidy figures for my accountant.

The code you deliver should:
1. Slot into the current Laravel-based API (MySQL) with minimal refactor.
2. Re-use our POS transaction data; don’t break current endpoints.
3. Include clear migration scripts, seed data for testing and concise setup notes.
4. Arrive unit-tested so I can validate GL entries, AP/AR aging and reconciliation logic.

I’m looking for someone who has built or heavily customised an accounting module before—please share a brief example or repo link when you respond.