The bugs that hurt a point of sale never show up in a demo.

What’s inside

Everything in Building a Production POS in ASP.NET Core.

• The double charge — idempotency keys enforced by a unique index
• Half a sale — one transaction, and receipt numbers with no gaps
• The last unit — a conditional, row-locked UPDATE instead of check-then-write
• Stock as a ledger — and weighted-average cost in one SQL statement
• Multi-tenancy — EF Core query filters that default to nothing
• Sign-in — short JWTs, rotating hashed refresh tokens and reuse detection
• Permissions — without privilege escalation
• Audit — a log nobody can edit, not even the owner
• Billing webhooks — signed, time-limited and de-duplicated
• Shipping it — tests against a real SQL Server, Docker, health checks, backups — and a one-page checklist